A three-level flexible excitation dynamic regulation method and system for large hydroelectric generating units

Abstract

The application discloses a three-level flexible excitation dynamic regulation method and system for large hydroelectric generating units, relates to the technical field of flexible excitation control of large hydroelectric generating units, and comprises the following steps: setting a direct-current bus voltage, initializing a capacitor voltage and an excitation output level mapping relationship; collecting machine end operation parameters, constructing a disturbance identification model and outputting a disturbance level; setting an excitation voltage output gear according to the disturbance level, and controlling a capacitor voltage difference, so that dynamic voltage equalization is realized by modulating a midpoint duty cycle. The method sets a bus target voltage and constructs an excitation voltage output mapping, combines a disturbance level identification mechanism and a dynamic voltage equalization strategy, and realizes closed-loop linkage of disturbance sensing-voltage regulation-voltage difference control. The method effectively improves the identification accuracy of the system to light disturbance and strong disturbance, enhances the voltage stability and capacitor symmetry of the excitation system, reduces the overshoot risk, and improves the control robustness and safety of the system under extreme working conditions.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of flexible excitation control of large hydroelectric generating units, in particular to a three-level flexible excitation dynamic regulation method and system for large hydroelectric generating units. BACKGROUND

[0002] With the continuous development of large hydroelectric generating units towards high capacity, high reliability and high stability, the excitation system as the core part of the generator operation control, its performance is directly related to the grid voltage regulation, system stability and grid quality. The traditional excitation system mostly adopts two-level structure, the regulation speed and accuracy are limited, and it is difficult to adapt to the dynamic demand of modern hydroelectric generating units under multi-working condition switching, high frequency disturbance and large range power fluctuation. In order to improve the excitation regulation response efficiency, three-level flexible excitation structure is gradually introduced, which realizes finer granularity regulation ability through multi-gear voltage control and dynamic current limiting. However, the dynamic coordination control and voltage balance management of three-level system still face engineering difficulties, especially in disturbance identification, gear switching and energy storage unit voltage balance control, there is a lack of systematic and robust regulation method.

[0003] The existing three-level excitation control technology mainly relies on static threshold or preset strategy for excitation voltage gear switching under multi-working condition operation condition, and cannot accurately identify and adaptively adjust according to the system disturbance characteristics, resulting in response lag or over-control, and there are problems of low disturbance identification granularity and fuzzy classification. At the same time, the fixed PWM strategy is mostly used for voltage balance regulation of energy storage capacitor voltage difference, and there is a lack of midpoint modulation mechanism linked with the running state, especially in the strong excitation or excitation state, the capacitor voltage imbalance of upper and lower bridge arms is easy to occur, which causes waveform distortion or device stress aggravation. The traditional control scheme does not construct a quantitative model of disturbance evolution trend, and cannot realize the mapping reasoning between voltage, frequency, reactive power change and disturbance level, so as to lack enough identification accuracy to support multi-gear excitation regulation logic. In actual application, there are often problems such as insufficient excitation voltage regulation granularity, long-term deviation accumulation of capacitor voltage and unstable excitation response coupling, which seriously restricts the high reliable regulation ability of flexible excitation system. Therefore, a dynamic regulation method combining disturbance identification and midpoint bias control mechanism is urgently needed to improve the adaptability of excitation control system to disturbance, the real-time of voltage balance and the stability of overall operation. SUMMARY

[0004] In view of the above problems, the present application is proposed.

[0005] Therefore, the technical problem solved by the present application is that the existing three-level excitation regulation method has problems of low disturbance identification granularity, non-adaptive voltage regulation mode switching, and difficulty in real-time regulation of capacitor voltage imbalance, and how to construct a three-level excitation dynamic regulation method combining disturbance identification and voltage balance linkage.

[0006] To solve the above technical problems, the application provides the following technical scheme: a three-level flexible excitation dynamic regulation method for large hydroelectric generating units, comprising setting a DC bus voltage, initializing a capacitor voltage and an excitation output level mapping relationship; collecting machine end operation parameters, constructing a disturbance identification model and outputting a disturbance level; setting an excitation voltage output gear according to the disturbance level and controlling a capacitor voltage difference, and realizing dynamic voltage balancing through modulation of a midpoint duty cycle; the construction of the disturbance identification model comprises collecting machine end operation parameters, outputting a change between the machine end operation parameters and a steady-state reference value, constructing a disturbance identification model, dividing a disturbance level in combination with an instantaneous amplitude of the change, and outputting a disturbance level identification value; the realization of dynamic voltage balancing through modulation of the midpoint duty cycle comprises, in the process of excitation voltage output, real-time collection of voltage values of upper and lower end capacitors of an energy storage capacitor bank, output of a capacitor voltage difference and a relative voltage difference ratio, judgment of whether the voltage difference ratio exceeds a safety threshold, and if yes, entering a dynamic voltage balancing state and controlling a duty cycle offset of a midpoint bridge arm of a PWM modulator.

[0007] As a preferred scheme of the three-level flexible excitation dynamic regulation method for large hydroelectric generating units, the setting of the DC bus voltage comprises that the set DC bus voltage is not lower than twice the rated excitation output voltage, and the capacitor bank voltage is initialized in the excitation system starting stage to make the upper and lower bridge arm capacitor voltages equal, and a proportional mapping relationship between the excitation output voltage and the target bus voltage is constructed.

[0008] As a preferred scheme of the three-level flexible excitation dynamic regulation method for large hydroelectric generating units, the collection of the machine end operation parameters comprises collection of a generator end voltage, a frequency, active power and reactive power.

[0009] As a preferred scheme of the three-level flexible excitation dynamic regulation method for large hydroelectric generating units, the disturbance level comprises output of a disturbance level identification value through construction of a disturbance identification model based on multi-parameter threshold comparison.

[0010] As a preferred scheme of the three-level flexible excitation dynamic regulation method for large hydroelectric generating units, the setting of the excitation voltage output gear according to the disturbance level comprises, in each control period, selection of a preset excitation voltage output gear parameter according to the disturbance level.

[0011] As a preferred scheme of the three-level flexible excitation dynamic regulation method for large hydroelectric generating units, the realization of dynamic voltage balancing through modulation of the midpoint duty cycle comprises, through real-time sampling of upper and lower bridge arm energy storage capacitor voltages and output of a voltage difference, adjustment of the midpoint duty cycle to realize dynamic voltage balancing when the voltage difference exceeds a set threshold.

[0012] As a preferred scheme of the three-level flexible excitation dynamic regulation method for large hydroelectric generating units, the modulation midpoint duty cycle comprises adaptive adjustment according to the differential ratio, and the control range is between the set minimum and maximum duty cycles.

[0013] Another object of the present application is to provide a three-level flexible excitation dynamic regulation system for large hydroelectric generating units, which can set the excitation voltage output gear according to the disturbance level and control the capacitor voltage difference, and realize dynamic voltage balancing through modulation midpoint duty cycle, thereby solving the problem that the current three-level excitation regulation method contains capacitor voltage imbalance which is difficult to adjust in real time.

[0014] As a preferred scheme of the three-level flexible excitation dynamic regulation system for large hydroelectric generating units, the system comprises an excitation initial voltage configuration module, a disturbance level identification modeling module, and an excitation voltage dynamic regulation and voltage balancing control module; the excitation initial voltage configuration module is used to set the voltage reference standard of the starting state of the excitation system; the disturbance level identification modeling module is used to judge the operating state of the generator and classify the disturbance level, construct a disturbance identification model and output a disturbance level identification by sampling parameters, and serve as the trigger basis for control strategy switching; and the excitation voltage dynamic regulation and voltage balancing control module is used to select the excitation voltage output gear according to the disturbance level and maintain the symmetry of the capacitor voltage.

[0015] A computer device comprises a memory and a processor, the memory stores a computer program, and the processor executes the computer program to implement the steps of the three-level flexible excitation dynamic regulation method for large hydroelectric generating units.

[0016] A computer readable storage medium stores a computer program, and the computer program is executed by a processor to implement the steps of the three-level flexible excitation dynamic regulation method for large hydroelectric generating units.

[0017] The three-level flexible excitation dynamic regulation method for large-scale hydroelectric generating units provided by the application realizes fine control and high reliable operation of the excitation system under multiple working conditions by constructing a three-level flexible excitation regulation method integrating initialization configuration, disturbance identification and dynamic voltage balancing. First, the target voltage of the DC bus is set and the capacitor voltage is initialized, thereby effectively constructing the mapping relationship between the excitation output level and the bus reference, establishing a clear and controllable output range and symmetric reference for subsequent voltage regulation. Key operating parameters such as terminal voltage, frequency and reactive power are collected, and a disturbance trend identification model is constructed in combination with the steady-state reference value, which not only improves the accuracy and robustness of disturbance level division, but also realizes rapid identification from steady state, light disturbance to strong excitation and de-excitation, driving the regulation system to adaptively switch the excitation level. In the regulation execution stage, a midpoint duty ratio adjustment mechanism based on pressure difference ratio is introduced to realize dynamic voltage balancing control and ensure voltage output stability and device symmetry. BRIEF DESCRIPTION OF DRAWINGS

[0018] In order to more clearly illustrate the technical solutions of the embodiments of the application, the following will briefly introduce the drawings needed to be used in the embodiment description. Obviously, the drawings in the following description are only some embodiments of the application, and other drawings can be obtained by those skilled in the art without creative labor.

[0019] Fig. 1 The overall flowchart of the three-level flexible excitation dynamic regulation method for large-scale hydroelectric generating units provided by the embodiment 1 of the application is shown in the figure.

[0020] Fig. 2 The overall structure diagram of the flexible excitation system of the large-scale hydroelectric generating unit of the three-level flexible excitation dynamic regulation method for large-scale hydroelectric generating units provided by the embodiment 1 of the application is shown in the figure. DETAILED DESCRIPTION

[0021] In order to make the above-mentioned objects, features and advantages of the application more obvious and easy to understand, the specific embodiments of the application will be described in detail below with reference to the drawings of the specification. Obviously, the described embodiments are part of the embodiments of the application, rather than all the embodiments. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative labor should be within the protection scope of the application.

[0022] Embodiment 1, refer to Figs. 1-2 For an embodiment of the application, a three-level flexible excitation dynamic regulation method for large-scale hydroelectric generating units is provided, which comprises:

[0023] S1: Set the DC bus voltage, initialize the capacitor voltage and the excitation output level mapping relationship.

[0024] Further, in view of the actual demand of the excitation system of a large hydroelectric generating unit for strong excitation, de-excitation and bidirectional switching, the target voltage of the DC bus of the excitation system is first set . The target voltage should meet the maximum voltage output demand covering the normal operation voltage, the fault strong excitation output voltage and the reverse de-excitation, and therefore needs to be set to more than 2 times the rated excitation voltage, with a certain dynamic control margin, which is expressed as:

[0025] ,

[0026] wherein, is the rated excitation voltage of the excitation winding of the generator; is the margin voltage for supporting the strategy adjustment of rapid voltage rise under fault conditions, and the recommended value range is .

[0027] If there is a low-frequency resonance risk in the system, the may be adjusted to leave a damping margin for oscillation. The target voltage is provided by the front three-level PWM converter, and the controller adjusts the output through a linear boost slope controller, to ensure that the DC voltage is smoothly boosted to the target value at the initial stage of system power-on, avoiding the non-steady-state start phenomenon caused by capacitor overcharging or dramatic changes in the magnetic field.

[0028] It should be noted that, considering that the three-level topology needs to provide multiple output ranges of positive, negative, half voltage and zero voltage at both ends of the chopper, two groups of energy storage capacitors (C1, C2) are used in series to form a voltage dividing structure of the DC bus voltage. After the system is powered on, active voltage balancing adjustment of the capacitors is started, which is expressed as:

[0029] ,

[0030] wherein, is the DC bus voltage of the capacitor C1, is the DC bus voltage of the capacitor C2.

[0031] The controller samples the voltages at both ends of C1 and C2 in real time, controls the midpoint conduction behavior of the front PWM through differential comparison, and makes the two capacitor groups maintain a voltage difference of not more than in the initial steady state. In engineering implementation, the following control logic can be used:

[0032] If , the conduction duty cycle of the C2 branch is increased to allow it to absorb more electric charge;

[0033] If , the midpoint offset is adjusted to moderately increase the charging rate of C1;

[0034] If (suggestion ), where is the capacitance voltage difference control threshold, that is, the maximum voltage deviation limit between the upper and lower bridge arm energy storage capacitors C1 and C2. Then the current PWM strategy remains unchanged, and the voltage locking state is entered.

[0035] In addition, an alarm mechanism needs to be triggered when the capacitance voltage difference fluctuates sharply to prevent voltage distortion caused by midpoint deviation.

[0036] It should be noted that after the bus voltage and capacitor voltage initialization is completed, the system enters the initialization configuration phase of the excitation output gear. To meet various operating requirements, the chopper output end is preset with multiple excitation voltage gears, and a mapping relationship table between them and the bus voltage is constructed, as shown in Table 1:

[0037] Table 1 Mapping relationship table

[0038]

[0039] The controller presets the above gears as state diagram nodes, and sets the following state transition rules: in the initial stage of normal power-on, the "zero voltage gear" is entered by default; after the bus voltage difference stabilizes, the "half voltage gear" is entered for maintenance; when the state recognition module outputs a fault signal or the frequency jumps, it can jump to the "strong excitation gear" or the "reverse gear"; the holding time or duty cycle of any gear is constrained by the protection logic to prevent long-term one-way output from damaging the chopper devices.

[0040] S2: Collect machine-side operating parameters, construct a disturbance recognition model and output the disturbance level.

[0041] Further, during the operation of the hydroelectric generating set, the excitation system needs to have high-speed sensing capability for the state changes of the external power grid and its own excitation circuit. This step first constructs a high-frequency operating state sampling framework, with a sampling period of 10ms-50ms, which can be adjusted according to the system response characteristics.

[0042] It should be noted that the collected machine-side operating parameters include generator terminal voltage, system frequency, generator electrical power angle, excitation current, generator port reactive power, rotor mechanical angular velocity, and energy storage capacitor temperature. After each sampling period ends, the system writes the sampling values into the buffer area for the state judgment module to call.

[0043] Based on the machine-side operating parameters, the system defines the disturbance index change as:

[0044] ,

[0045] wherein represents the parameter in the time window The change amount (difference) of the internal, representing the transient offset amplitude of the current change trend, The current time The real-time value of a certain operating parameter (such as voltage, frequency, reactive power, etc.) collected, The sliding time window or lag time amount, in seconds (s), is usually taken as 0.5s, 1s, 2s, etc. The historical value of the parameter at the current time Tracing back seconds.

[0046] It should also be noted that the disturbance trend integral function As a comprehensive disturbance measurement index:

[0047] ,

[0048] Where, The disturbance trend integral value at the current time , representing the cumulative strength of the integrated disturbance of the system in the near future, The disturbance observation time window length, in seconds (s), such as 1s or 2s, represents the cumulative evaluation of the disturbance in the past seconds, The change amount of the terminal voltage at time point , The change amount of the frequency at time point , The change amount of the reactive power at time point , is an empirical weight factor, used to balance the contribution of voltage, frequency, and power to the disturbance trend;

[0049] When , the disturbance level is determined to be steady-state operation; when , the disturbance level is determined to be light disturbance; when , the disturbance level is determined to be strong disturbance; when , the disturbance level is determined to be extreme disturbance (strong excitation, de-excitation).

[0050] In addition, the system can call the disturbance evolution prediction module to forward infer the voltage and frequency change trend for the next period, to assist in entering the strong excitation or de-excitation mode in advance.

[0051] The identified disturbance type is bound to the excitation control state machine to construct a state-action mapping structure table, as shown in Table 2:

[0052] Table 2 State-Action Mapping Structure Table

[0053]

[0054] The system records the following information when identifying state changes: state switching timestamp; state duration; main cause analysis of the triggering disturbance; difference vector from the previous state.

[0055] S3: Set the excitation voltage output gear according to the disturbance level, control the capacitor voltage difference, and achieve dynamic voltage balancing by modulating the midpoint duty cycle.

[0056] Furthermore, the system determines the current excitation control mode according to the disturbance identification result of S2 in each control cycle (typical value: 5-10 ms).

[0057] It should be noted that the excitation output control is based on the set target voltage , the current output voltage is adjusted to achieve fast tracking. The basic control model is as follows:

[0058] ,

[0059] wherein, is the output voltage gear coefficient set according to the current mode;

[0060] In the strong excitation mode, if there is a bus voltage drop (such as a voltage drop caused by dynamic load of the chopper), voltage drop compensation needs to be introduced:

[0061] ,

[0062] wherein, the voltage drop compensation term can be estimated by the voltage deviation model:

[0063] ,

[0064] wherein, is an empirical gain coefficient (usually ), used to quickly compensate for the weakening effect of bus voltage drop on excitation voltage output.

[0065] To avoid current overshoot damage to excitation windings or chopper devices in the strong excitation state, the present application introduces a current limiting controller, sets a current limit threshold , and establishes a limiting adjustment function based on output voltage feedback:

[0066] ,

[0067] wherein, is the equivalent impedance of the excitation circuit (which can be measured or calibrated).

[0068] If is measured, the current is temporarily weakened , reduce the output gear, wait for the current to drop and then slowly rise; the current limiter has a differential prediction mechanism to avoid transient current peak over-limit when the voltage is quickly boosted.

[0069] The minimum hold time limit is introduced, as shown in Table 3:

[0070] Table 3 Time limit table

[0071]

[0072] In addition, to improve the smoothness of dynamic switching, a step transition buffer is set: any switching between two different voltage levels must be controlled by a linear slope, and the slope time constant is set to 20-50 ms to avoid system instability caused by large excitation disturbance.

[0073] The system synchronously collects the current voltage values of the two capacitors in each control cycle and , calculate the voltage difference:

[0074] ,

[0075] and compared with half of the bus reference voltage , the relative voltage difference ratio is established:

[0076] ,

[0077] wherein, represents the relative voltage difference ratio.

[0078] If , it is considered that the voltage difference enters the controllable range, wherein the voltage difference threshold is usually set to , and exceeds this value, it enters the asymmetric voltage sharing control state.

[0079] It should be noted that once , the control system enters the active voltage sharing state, by adjusting the PWM midpoint bias pulse width, changing the charging and discharging path of C1 and C2, the target is to converge . If , increase the conduction time of the midpoint to C2, and the duty cycle is adjusted to . If , increase the conduction ratio of the midpoint to the C1 branch, and handle symmetrically; the midpoint offset adjustment is constrained within to avoid frequent bias causing output waveform distortion.

[0080] The PWM modulator can use adaptive dead zone adjustment logic according to The delay time of the midpoint bridge arm is adjusted in real time to achieve microsecond-level voltage sharing control accuracy.

[0081] Considering that the charge and discharge cycles and amplitude differences of C1 and C2 are large in different excitation modes, the voltage sharing control needs to have mode adaptability. The voltage sharing rate is dynamically enhanced in strong excitation and de-excitation modes.

[0082] ,

[0083] Among them, represents an effective voltage regulation coefficient, represents a basic voltage regulation coefficient, is a steady state, is a light disturbance, is strong excitation and de-excitation.

[0084] This mechanism ensures that the voltage symmetry of C1 and C2 can be quickly restored under a short-time high-current impact, improves the gear output stability, and avoids overcharging or breakdown of a single capacitor.

[0085] If the system continuously detects for more than 100 ms, an abnormal pressure difference alarm state is entered, and the system performs the following protection actions: reducing the excitation output level, switching from the strong excitation gear to the half-pressure gear or the zero-pressure gear, outputting a fault event code, starting a bypass discharge branch or a reserved redundant capacitor to participate in voltage sharing, and if the balance cannot be restored, issuing a high-level protection shutdown signal and recording waveform data.

[0086] In addition, the system allows reading the recent pressure difference record during the shutdown and restart process, and delaying the initialization of the strong excitation gear to avoid the amplification effect of imbalance again in the power-on overshoot state.

[0087] Embodiment 2, one embodiment of the present application, provides a three-level flexible excitation dynamic regulation method for large hydroelectric generating units. In order to verify the beneficial effects of the present application, economic benefit calculation and simulation experiments are carried out for scientific demonstration.

[0088] Firstly, an excitation system comparative experiment framework based on a simulation platform and a semi-physical experimental device is constructed. The test objects include two types of systems: a traditional double-level excitation control system and a three-level flexible excitation system designed according to the present application. The test platform includes an excitation system controller, a chopper module, an energy storage capacitor group, a PWM modulator and a simulation generator model. The system is connected with a high-precision data acquisition unit through a PLC, and the sampling period is set to 10 ms to simulate the response characteristics under different disturbance levels.

[0089] Firstly, the initialization settings of the two systems are completed respectively. The traditional system sets a single rated bus voltage, while the system of the present application sets a bus target voltage according to twice the rated excitation voltage of the generator, and initializes the capacitor voltage difference threshold and midpoint modulation control logic. In the starting stage, the system of the present application activates the linear boost slope adjustment mechanism to realize dynamic voltage equalization of C1 and C2, and completes the preset mapping of the voltage gear.

[0090] In the disturbance simulation stage, three types of disturbances are injected respectively: light disturbance (such as small amplitude grid voltage sag), strong disturbance (such as main transformer fault, electrical angle mutation) and de-excitation condition (manually triggered loss-of-step protection). The operating parameters including voltage, frequency, current, reactive power, power angle and other indicators are collected, the disturbance level is automatically judged by the disturbance identification model, and different excitation output gears are dispatched. In the experiment, the trigger threshold (for example, Δf ≥ 0.3Hz is judged as strong disturbance) is set, and the response time, voltage recovery process, capacitor voltage difference and midpoint offset are recorded according to the corresponding rules.

[0091] During the experiment, the key indicators such as current overshoot limitation effect, voltage recovery time and voltage equalization success rate are observed, and the system response and balance stability under three disturbance levels are recorded to build a basis for comparison and evaluation. The experimental data is shown in Table 4.

[0092] Table 4 Experimental data table

[0093]

[0094] From the experimental data, it can be observed that under the three types of disturbance conditions, the three-level flexible excitation system of the present application is superior to the traditional excitation system in various performance indicators. For example, under light disturbance, the average excitation response time of the traditional system is 74.2ms, while that of the system of the present application is shortened to 48.7ms, indicating that the disturbance identification mechanism has a significant advantage in response speed; and under strong disturbance, the response time is shortened from 128.9ms to 91.5ms, reflecting that the dynamic regulation mechanism based on disturbance level can effectively speed up the regulation process.

[0095] In addition, in terms of maximum capacitor voltage difference, the traditional system has a voltage difference of 12.5% under de-excitation state, while the system of the present application controls the voltage difference within 3.9% by introducing the midpoint duty ratio modulation mechanism and the voltage equalization threshold judgment mechanism, which proves that the dynamic voltage equalization regulation strategy can realize fast voltage difference convergence and significantly improve the symmetry of the capacitor bank. The success rate of voltage equalization also proves the practicality of the strategy: from 73.6% to 96.8% under de-excitation state.

[0096] In terms of current overshoot control, the system of the application automatically suppresses current peaks through a current limiting regulation function, suppressing the maximum current from 76.4 A to 49.7 A in the case of strong disturbance, which embodies the effectiveness of the limiting mechanism based on feedback current closed-loop regulation in protecting equipment. The improvement in voltage recovery time further demonstrates the advantages of flexible voltage level setting.

[0097] In summary, by establishing the three-step collaborative mechanism of bus voltage initial control, disturbance level identification, and integrated control of dynamic voltage output and voltage equalization, the method of the application exhibits superior performance in key dimensions such as response speed, voltage equalization accuracy, and system stability. The core innovation lies in: first introducing a disturbance trend integral function as a disturbance level identification criterion, combining PWM midpoint duty cycle offset adjustment to achieve microsecond-level capacitor voltage equalization, and establishing a pressure difference closed loop and fault redundancy protection linkage mechanism, filling the coupling bottleneck problem between existing asymmetric capacitor control and multi-level excitation regulation. The test results fully demonstrate the engineering feasibility and practical value of the application.

[0098] In Example 3, an embodiment of the application provides a three-level flexible excitation dynamic regulation system for large hydroelectric generating units, including an excitation initial voltage configuration module, a disturbance level identification modeling module, and an excitation voltage dynamic regulation and voltage equalization control module.

[0099] The excitation initial voltage configuration module is used to set the voltage reference standard of the starting state of the excitation system, initialize the bus voltage and capacitor voltage distribution structure. The excitation initial voltage configuration module sets the target voltage of the DC bus covering regular operation and fault response according to the rated voltage of the excitation winding and the fault strong excitation / de-excitation requirement, and reserves a regulation margin. The excitation initial voltage configuration module further controls the linear boost slope of the front-stage three-level PWM converter, realizes the gradual increase of the bus voltage to the target value, and prevents capacitor overcharging and excitation mutation. After voltage initialization, the module establishes a midpoint symmetric regulation structure for the energy storage capacitor group C1 and C2, monitors the voltages of the two groups in real time, adjusts the midpoint duty cycle through capacitor voltage difference feedback control, ensures that the voltage difference between C1 and C2 is stable within the preset threshold, and outputs the excitation voltage reference curve and voltage difference equalization state to the disturbance level identification modeling module and the excitation voltage dynamic regulation and voltage equalization control module as the basis for subsequent strategies.

[0100] The disturbance level identification modeling module is used to collect generator operating state parameters and make disturbance level discrimination, providing basis for control strategy switching. The disturbance level identification modeling module takes the initialization parameters output by the excitation initial voltage configuration module as input premise, collects key indicators such as generator terminal voltage, system frequency, reactive power, and electrical power, constructs a sliding window difference model and a disturbance trend integral model, extracts parameter variation trend and comprehensive disturbance degree. The disturbance level identification modeling module judges the current operating state according to the set steady state, light disturbance, strong disturbance and extreme disturbance threshold, outputs the disturbance level identification, and is accompanied by state switching timestamp, main reason field, disturbance evolution prediction value and other diagnostic information. The disturbance level identification will be transmitted to the excitation voltage dynamic regulation and voltage control module as an input signal, guiding the selection of excitation voltage gear and the scheduling of voltage equalization behavior.

[0101] The excitation voltage dynamic regulation and voltage control module is used to receive the disturbance level identification and dynamically adjust the excitation output voltage and control the energy storage capacitor voltage difference under different working conditions, realizing stable and efficient excitation response. The module automatically selects the voltage output gear (such as strong excitation gear, half voltage gear, and excitation gear) based on the input information of the disturbance level identification modeling module, and adjusts the output voltage curve according to the current mode, realizing voltage fast tracking and voltage drop compensation. At the same time, the module obtains the terminal voltage of the energy storage capacitor C1 and C2 in real time, constructs a voltage difference feedback model, calculates the relative voltage difference ratio, and judges whether to enter the active voltage equalization control state. When the voltage difference exceeds the preset threshold, the module starts PWM midpoint bias adjustment, changes the branch conduction duty cycle, realizes voltage difference convergence control, and sets the midpoint offset slope and minimum holding time according to the excitation state, avoiding frequent switching and output distortion. The voltage equalization control logic supports adaptive adjustment of adjustment rate and control strategy under different disturbance levels, improving the system stability under high dynamic states such as strong excitation and excitation.

Claims

1. A three-level flexible excitation dynamic regulation method for large hydroelectric generating units, characterized in that, The method comprises the following steps: Set the DC bus voltage, initialize the capacitor voltage and the mapping relationship between the excitation output level; Collect the generator terminal operating parameters, build a disturbance identification model and output the disturbance level; The disturbance level comprises outputting the disturbance level identification value by building a disturbance identification model based on multi-parameter threshold comparison; The collected generator terminal operating parameters include generator terminal voltage, system frequency, generator electrical power angle, excitation current, generator port reactive power, rotor mechanical angular velocity and energy storage capacitor temperature, and after each sampling period, the sampling value is written into the buffer area for the state judgment module to call; Based on the generator terminal operating parameters, define the disturbance index change as: ， wherein, represents a parameter represents a change amount within a time window, a transient offset magnitude representing a current change trend, represents a real-time value of an operating parameter collected at a current time point, represents a sliding time window or a lag time amount, represents a historical value traced back seconds ago of the parameter; Introducing a perturbation trend integral function As a perturbation synthesis metric indicator: ， wherein, represents a disturbance trend integral value at the current time point , represents a disturbance observation time window length, represents a cumulative evaluation on the disturbance in the past seconds, represents a change amount of terminal voltage at the time point , represents a change amount of frequency at the time point , represents a change amount of reactive power at the time point , is an empirical weight factor for balancing the contribution of voltage, frequency and power to the disturbance trend. When the disturbance level is determined to be steady state operation; When , the disturbance level is determined to be a light disturbance; When , the disturbance level is determined to be a strong disturbance; When , the disturbance level is determined to be an extreme disturbance; According to the disturbance level, set the excitation voltage output gear, control the capacitor voltage difference, and realize dynamic voltage sharing by modulating the midpoint duty cycle; Building a disturbance identification model includes collecting generator terminal operating parameters, outputting the change between the collected generator terminal operating parameters and the steady-state reference value, building a disturbance identification model, dividing the disturbance level according to the instantaneous amplitude of the change, and outputting the disturbance level identification value; Realizing dynamic voltage sharing by modulating the midpoint duty cycle includes real-time sampling of the voltage values of the upper and lower end capacitors of the energy storage capacitor group during the excitation voltage output process, outputting the capacitor voltage difference and the relative voltage difference ratio, and judging whether the relative voltage difference ratio exceeds the safety threshold. If it is satisfied, enter the dynamic voltage sharing state and control the duty cycle offset of the midpoint bridge arm of the PWM modulator.

2. The three-level flexible excitation dynamic regulation method for large hydroelectric generating units according to claim 1, characterized in that: The set DC bus voltage includes The set DC bus voltage is not less than twice the rated excitation output voltage, and the capacitor group voltage is initialized during the excitation system starting stage to make the upper and lower bridge arm capacitor voltages equal, and the proportional mapping relationship between the excitation output voltage and the target bus voltage is built.

3. The three-level flexible excitation dynamic regulation method for large hydroelectric generating units according to claim 2, characterized in that: The collected generator terminal operating parameters include Generator terminal voltage, frequency, active power and reactive power.

4. The three-level flexible excitation dynamic regulation method for large hydroelectric generating units according to claim 3, characterized in that: According to the disturbance level, set the excitation voltage output gear includes In each control period, according to the disturbance level, select the preset excitation voltage output gear parameter.

5. The three-level flexible excitation dynamic regulation method for large hydroelectric generating units according to claim 4, characterized in that: Realizing dynamic voltage sharing by modulating the midpoint duty cycle includes Real-time sampling of the upper and lower bridge arm energy storage capacitor voltage and outputting the relative voltage difference ratio, adjusting the midpoint duty cycle to realize dynamic voltage sharing when the relative voltage difference ratio exceeds the set threshold.

6. The three-level flexible excitation dynamic regulation method for large hydroelectric generating units according to claim 5, characterized in that: The modulation of the midpoint duty cycle includes Adaptive adjustment according to the voltage difference ratio, the control range is between the set minimum and maximum duty cycles.

7. A three-level flexible excitation dynamic regulation system for large hydroelectric generating units, which adopts the three-level flexible excitation dynamic regulation method for large hydroelectric generating units according to any one of claims 1-6, characterized in that: The method comprises an excitation initial voltage configuration module, a disturbance level identification modeling module, and an excitation voltage dynamic regulation and voltage sharing control module. The excitation initial voltage configuration module is used to set the voltage reference standard of the starting state of the excitation system; The disturbance level identification modeling module is used to judge the generator operating state and classify the disturbance level, sample the parameters, build a disturbance identification model and output the disturbance level identification, which is used as the trigger basis for control strategy switching; The excitation voltage dynamic regulation and voltage sharing control module is used to select the excitation voltage output gear according to the disturbance level and maintain the symmetry of the capacitor voltage.

8. A computer device comprising a memory and a processor, the memory storing a computer program, characterized in that, The processor executes the computer program to realize the steps of the three-level flexible excitation dynamic regulation method for large hydroelectric generating units in any one of claims 1 to 6.

9. A computer readable storage medium having stored thereon a computer program, characterized in that, The computer program is executed by a processor to realize the steps of the three-level flexible excitation dynamic regulation method for large hydroelectric generating units according to any one of claims 1 to 6.

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