Grid-connected control method and system applied to static frequency converter

Abstract

The application relates to a grid-connected control method and system applied to a static frequency converter. The method comprises the following steps: obtaining a power grid operation state and a unit operation state; obtaining a corresponding rotating speed of the unit; obtaining a corresponding unit terminal phase and a unit terminal amplitude based on the unit operation state and obtaining a corresponding power grid phase and a power grid amplitude of the power grid based on the power grid operation state after the corresponding rotating speed of the unit reaches a preset rotating speed; obtaining a phase difference between the unit terminal phase and the power grid phase and an amplitude difference between the unit terminal amplitude and the power grid amplitude; adjusting the corresponding operation state of the unit based on the phase difference and the amplitude difference; and when the phase difference and the amplitude difference corresponding to the adjusted operation state satisfy a preset condition, issuing a grid-connected instruction after blocking a trigger pulse of the static frequency converter, so that an external device connects the unit to the power grid in response to the grid-connected instruction. The method can improve the efficiency of unit grid connection and the integration of the system.

Description

Technical Field

[0001] This application relates to the field of power technology, and in particular to a grid-connected control method, system, computer equipment, computer-readable storage medium, and computer program product applied to a static frequency converter. Background Technology

[0002] With the development of power grids, the operating characteristics of pumped storage units have also changed, with short-time, frequent starts becoming a new trend in power plant operation. This places higher demands on the unit's start-up response speed, reliability, and control precision.

[0003] In existing technologies, external synchronizing devices are typically used to connect the generating units to the grid. However, this may introduce additional communication links and points of failure, thereby affecting the efficiency of grid connection. Summary of the Invention

[0004] Therefore, it is necessary to provide a grid-connected control method, device, computer equipment, computer-readable storage medium, and computer program product for static frequency converters that can improve the grid connection efficiency of the unit and enhance the system integration, in order to address the aforementioned technical problems.

[0005] In a first aspect, this application provides a grid-connected control method for a static frequency converter, including:

[0006] Obtain the power grid operating status and generator operating status; obtain the corresponding speed of the generator;

[0007] After controlling the rotational speed of the generator unit to reach the preset rotational speed, the generator terminal phase and generator terminal amplitude are obtained based on the generator unit's operating state, and the grid phase and grid amplitude are obtained based on the grid's operating state.

[0008] The phase difference between the generator terminal phase and the grid phase, and the amplitude difference between the generator terminal amplitude and the grid amplitude are obtained; the operating state of the generator unit is adjusted based on the phase difference and the amplitude difference.

[0009] When the phase difference and amplitude difference corresponding to the adjusted operating state meet the preset conditions, after blocking the trigger pulse of the static inverter, a grid connection command is issued so that the external device responds to the grid connection command to connect the unit into the power grid.

[0010] In one embodiment, obtaining the rotational speed of the generator unit includes: obtaining a first rotational speed of the generator unit using physical sensors installed on the generator unit; obtaining voltage information of the generator unit based on the operating state of the generator unit; obtaining a second rotational speed of the generator unit based on the voltage information; determining a target rotational speed range in which the first rotational speed is located from a first rotational speed range, a second rotational speed range, and a third rotational speed range; wherein the maximum rotational speed of the first rotational speed range is less than the minimum rotational speed of the second rotational speed range, and the maximum rotational speed range of the second rotational speed range is less than the minimum rotational speed of the third rotational speed range; if the target rotational speed range is the first rotational speed range, determining the rotational speed of the generator unit based on the first rotational speed; if the target rotational speed range is the third rotational speed range, determining the rotational speed of the generator unit based on the second rotational speed.

[0011] In one embodiment, adjusting the operating state of the generator unit based on the phase difference and the amplitude difference includes: inputting the phase difference to a phase closed-loop controller to calculate a frequency correction amount, and superimposing the frequency correction amount onto the current base output frequency of the static inverter to dynamically adjust the output frequency state of the static inverter so that the phase of the generator terminal voltage tracks the phase of the grid voltage; inputting the amplitude difference to an amplitude closed-loop controller to calculate an excitation current correction amount, and superimposing the excitation current correction amount onto the current base excitation current of the excitation device to dynamically adjust the excitation current state of the generator unit so that the amplitude of the generator terminal voltage tracks the amplitude of the grid voltage.

[0012] In one embodiment, controlling the rotational speed of the unit to reach a preset rotational speed includes: if the rotational speed is in a low-speed range, acquiring the stator current output by the static inverter and controlling the amplitude of the stator current to clamp to a preset maximum current threshold; if the rotational speed is in a medium-speed range, acquiring the slope deviation between the rotational speed and a preset acceleration curve, and adjusting the rate of change of the output frequency of the static inverter based on the slope deviation; if the rotational speed is in a high-speed range, acquiring the residual between the rotational speed and the preset rotational speed, obtaining the adjustment amount corresponding to the output frequency based on the residual, and adjusting the output frequency based on the adjustment amount so that the rotational speed converges to the preset rotational speed.

[0013] In one embodiment, when the phase difference and amplitude difference corresponding to the adjusted operating state meet preset conditions, after blocking the trigger pulse of the static inverter, a grid connection command is issued, including: obtaining the inherent mechanical closing time of the external device and the extinction time required for the current of the static inverter to decay to zero after executing the blocking trigger pulse action; summing the mechanical closing time and the extinction time to obtain the comprehensive lead time; converting the comprehensive lead time into the corresponding target lead phase angle based on the frequency difference between the unit and the grid; when the phase difference monitored in real time decays to be equal to the target lead phase angle, executing the action of blocking the trigger pulse of the static inverter, and issuing the grid connection command after the extinction time has elapsed.

[0014] In one embodiment, the method further includes: obtaining the absolute value of the frequency difference between the generator frequency and the grid frequency, and the phase difference change rate over time; determining whether the absolute value of the frequency difference is greater than a preset grid disturbance threshold; if it is greater than the grid disturbance threshold, increasing the proportional gain of the phase closed-loop controller based on the phase difference change rate and shortening the integral time constant; calculating a frequency correction amount based on the adjusted proportional gain and integral time constant, and adjusting the output frequency of the static inverter based on the frequency correction amount.

[0015] Secondly, this application also provides a grid-connected control device for a static frequency converter, comprising:

[0016] The signal detection module is used to acquire the power grid operating status and the unit operating status;

[0017] The speed observation module is used to obtain the unit's operating status from the signal detection module and obtain the corresponding rotational speed of the unit based on the unit's operating status.

[0018] The control module is used to acquire the rotational speed measured by the speed observation module, and after controlling the rotational speed of the unit to reach a preset rotational speed, obtain the generator terminal phase and generator terminal amplitude of the unit based on the unit operating status acquired from the signal detection module, and obtain the grid phase and grid amplitude of the grid based on the grid operating status acquired from the signal detection module; acquire the phase difference between the generator terminal phase and the grid phase, and the amplitude difference between the generator terminal amplitude and the grid amplitude; adjust the operating status of the unit based on the phase difference and the amplitude difference, so that when the phase difference and amplitude difference of the adjusted operating status meet preset conditions, a first grid connection command is issued;

[0019] The grid connection module is used to block the trigger pulse of the static inverter in response to the first grid connection command, and then issue a second grid connection command so that the external device responds to the second grid connection command to connect the unit to the power grid.

[0020] Thirdly, this application also provides a computer device, including a memory and a processor, wherein the memory stores a computer program, and the processor executes the computer program to implement the steps described in the above method embodiments.

[0021] Fourthly, this application also provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps described in the above method embodiments.

[0022] Fifthly, this application also provides a computer program product, including a computer program that, when executed by a processor, implements the steps described in the above method embodiments.

[0023] The aforementioned grid-connection control method, device, computer equipment, computer-readable storage medium, and computer program product applied to static frequency converters (SFDs) calculate phase and amplitude differences by acquiring the grid and unit operating states through the control system applied to the SFD, and dynamically adjusts the unit operating state based on these differences. This eliminates the need for traditional external synchronization devices and cross-system communication interactions, achieving a high degree of integration of synchronization functions and significantly reducing grid-connection response delay, thereby improving grid-connection efficiency. Furthermore, by issuing a grid-connection command after blocking the trigger pulse of the SFD, the harmonic current path of the SFD can be cut off from its physical source before the closing moment, thereby reducing circulating current hazards and electrical shocks caused by grid-connection operations. This enables safe, accurate, and rapid smooth grid connection in high-frequency start-up scenarios for pumped storage units. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of this application or related technologies, the drawings used in the description of the embodiments of this application or related technologies will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 This is a flowchart illustrating a grid-connected control method applied to a static frequency converter in one embodiment;

[0026] Figure 2 This is a flowchart illustrating the steps for obtaining the unit's rotational speed in one embodiment;

[0027] Figure 3 This is a flowchart illustrating the steps for adjusting the operating status of a generator unit based on phase difference and amplitude difference in one embodiment.

[0028] Figure 4 This is a flowchart illustrating the steps before the control unit reaches a preset speed in one embodiment.

[0029] Figure 5 This is a flowchart illustrating the steps of issuing a grid connection command after blocking the trigger pulse of the static inverter in one embodiment.

[0030] Figure 6 This is a flowchart illustrating the steps for adjusting the output frequency in one embodiment;

[0031] Figure 7 This is a schematic diagram of the architecture of a grid-connected control system applied to a static frequency converter in one embodiment;

[0032] Figure 8 This is a flowchart illustrating a grid-connected control method applied to a static frequency converter in another embodiment;

[0033] Figure 9 This is a structural block diagram of a grid-connected control device applied to a static frequency converter in one embodiment;

[0034] Figure 10 This is an internal structural diagram of a computer device in one embodiment. Detailed Implementation

[0035] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0036] The grid-connected control method for static frequency converters (SFCs) provided in this application embodiment allows the power grid to be connected to the grid-side converter (rectifier bridge) of the SFC via a dedicated input circuit breaker and step-down transformer in its application environment. Simultaneously, a direct main path exists between the power grid and the generating unit, with a generator output circuit breaker (GCB) connected in series along this path; however, this circuit breaker is in an open state during startup. The SFC acts as an intermediate bridge between the power grid and the generating unit. The SFC's generator-side converter can be connected to the three-phase windings of the generator stator via an output circuit breaker and step-up transformer. The control system applied to the SFC can control the grid connection process between the power grid and the generating unit.

[0037] In one exemplary embodiment, such as Figure 1As shown, a grid-connected control method for a static frequency converter is provided. Taking the application of this method to a static frequency converter as an example, the method includes the following steps 102 to 108. Wherein:

[0038] Step 102: Obtain the grid operation status and the unit operation status; obtain the corresponding speed of the unit.

[0039] The grid operating status refers to the set of electrical parameters on the grid side, including at least grid voltage, frequency, and phase. The generator operating status refers to the set of electrical and mechanical parameters on the generator motor side driven by the static frequency converter (SFC). The rotational speed refers to the current mechanical rotational speed of the generator rotor as measured.

[0040] In some embodiments, the unit's rotational speed can be obtained directly from physical sensors installed on the unit side. In other embodiments, the unit's rotational speed can be determined by combining the unit's electrical parameters with the rotational speed obtained from the physical sensors.

[0041] For example, voltage transformers are installed at the generator output and on the grid bus. These voltage transformers can proportionally reduce high voltage (tens of thousands of volts) to a low-voltage analog signal of a specified volt (e.g., 100V). A geared disc and a speed-measuring rotor are mounted on the generator shaft. Each time the rotor passes a tooth, the speed-measuring probe generates a weak pulse signal. The data acquisition board in the SFC control cabinet receives these analog and pulse signals. Then, the analog-to-digital converter inside the board divides the continuously changing voltage waveform into specific digital values ​​(e.g., a voltage of 53.2V at a given moment) at a frequency of several thousand times per second. Simultaneously, a counter records the number of pulses detected per second. The host computer (controller) then reads this data. The voltage values ​​are reconstructed into waveform curves to obtain the grid operating status and the generator operating status. To obtain the rotational speed based on the generator operating status, the number of pulses per second can be multiplied by a preset conversion factor. In other words, analog signals can be collected by voltage and current transformers installed at the generator terminals, and the generator pulse sequence can be obtained through speed measuring gears, thereby calculating the rotational speed and various state electrical quantities.

[0042] Optionally, obtaining the corresponding rotational speed of the generator set includes: obtaining the generator terminal voltage and stator current; calculating the rotor's electric angular velocity based on the generator terminal voltage and stator current using a preset motor state observation model; and determining the corresponding rotational speed of the generator set based on the electric angular velocity and the number of pole pairs of the generator set.

[0043] Step 104: After the speed of the control unit reaches the preset speed, obtain the generator terminal phase and generator terminal amplitude based on the unit's operating status, and obtain the grid phase and grid amplitude based on the grid's operating status.

[0044] Step 106: Obtain the phase difference between the generator phase and the grid phase, and the amplitude difference between the generator amplitude and the grid amplitude; adjust the corresponding operating state of the generator based on the phase difference and amplitude difference.

[0045] The preset speed refers to the threshold value close to the rated speed (e.g., 98% of the rated speed). The generator terminal phase / amplitude refers to the starting abscissa position and peak height of the sinusoidal voltage at the generator stator outlet. Similarly, the grid phase / amplitude refers to the position and height of the grid sinusoidal wave.

[0046] Adjusting the operating status refers to narrowing the gap between the unit's operating status and the grid's operating status by changing the output frequency and excitation current of the SFC.

[0047] Since fine-tuning of the unit's operating status is not necessary when the unit's operating speed is relatively low, a preset speed is first established. Once the unit reaches the preset speed, the operating status is then adjusted based on the difference between the grid's operating status and the unit's operating status.

[0048] For example, after acquiring the voltage signal corresponding to the generating unit or the power grid, the voltage signal is sent to a "zero-crossing comparator" chip. The function of this chip is to output a square wave at the moment the voltage changes from negative to positive and crosses zero. When the zero-crossing square wave corresponding to the generating unit is detected, a high-precision timer set in the SFC records the current time, obtaining a first time T1. When the zero-crossing square wave corresponding to the power grid is detected, the high-precision timer records the current time, obtaining a second time T2. Based on the first and second times respectively, the generating unit phase and the power grid phase are obtained. The difference between the generating unit phase and the power grid phase is then calculated to obtain the phase difference. In other embodiments, the difference between the second time and the first time can be obtained first, and then the phase difference can be obtained based on this difference. Specifically, the phase difference is obtained based on the difference between the second time and the first time and the frequency of the power grid.

[0049] For example, the acquired unit operating status may include the unit voltage detected by a voltage transformer. The maximum voltage can then be found from these voltages to determine the unit amplitude. Similarly, the grid amplitude can also be obtained. The difference between the grid amplitude and the unit amplitude is calculated to obtain the amplitude difference.

[0050] In some embodiments, the operating state of the generator unit can be adjusted based on a PID closed-loop controller. For example, a phase difference is input to a phase regulator, which calculates a speed adjustment based on the phase difference. The input adjustment is converted into a fine-tuning command for the SFC output frequency. Based on this fine-tuning command, the output frequency of the SFC is changed, thereby changing the generator speed to eliminate the phase difference. For amplitude adjustment, the amplitude difference can be sent to a voltage regulator, which calculates a current adjustment based on the amplitude difference. A setpoint for the excitation current of the excitation system is generated based on this current adjustment. Based on this setpoint, the generator terminal voltage is changed to eliminate the amplitude difference.

[0051] In other embodiments, a predictive model can be established based on the current phase difference and the unit's rotational angular acceleration. This predictive model forecasts the phase change trajectory over a future period. By comparing this phase change trajectory with the grid phase, the required frequency step adjustment and voltage feedforward compensation are calculated in advance and sent to the SFC's frequency output and excitation system to achieve rapid catch-up.

[0052] Step 108: When the phase difference and amplitude difference corresponding to the adjusted operating state meet the preset conditions, after blocking the trigger pulse of the static inverter, a grid connection command is issued so that the external device responds to the grid connection command and connects the unit to the grid.

[0053] The preset conditions refer to the safe threshold range for allowing closing, such as a phase difference less than a preset angle, an amplitude difference less than a preset voltage value, and the bed investment being able to continue for a preset time. The blocking trigger pulse refers to forcibly cutting off the gate drive signal of the thyristor inside the SFC, putting it in the off state. External devices refer to mechanical switching equipment (such as the generator output circuit breaker GCB) that performs the physical closing action.

[0054] For example, when both the phase difference and amplitude difference are less than a preset threshold, the digital I / O port inside the control system of the static inverter is immediately pulled low, and the pulse trigger channel to the SFC power cabinet is instantly cut off through fiber optic hardwiring to achieve blocking. Furthermore, an internal timer is started, delaying for a fixed period to ensure that the SFC current drops to zero and the circuit breaker mechanism's action time matches. Then, a high-level pulse is output through another digital I / O channel as a grid connection command to drive the closing coil of the external circuit breaker.

[0055] In other embodiments, the control system not only calculates the difference in real time, but also calculates the optimal leading phase angle based on historical data or measurements of the inherent mechanical closing time of the circuit breaker. That is, when the predicted phase difference reaches this leading phase angle, the system immediately sends a pulse blocking word through the underlying bus. After blocking confirmation, it accurately sends the grid connection command to an external device, which instantly triggers the circuit breaker to close upon receiving the message. This cancels out the time interval between sending the grid connection command and the actual grid connection, achieving seamless grid connection.

[0056] In the aforementioned grid-connected control method applied to static frequency converters, the control system applied to the static frequency converter obtains the grid and unit operating status to calculate the phase difference and amplitude difference, and dynamically adjusts the unit operating status based on these phase and amplitude differences. This eliminates the need for traditional external synchronization devices and cross-system communication interaction, achieving a high degree of integration of synchronization functions and significantly reducing grid-connected response delay, thereby improving grid-connected efficiency. Furthermore, by issuing the grid-connected command after blocking the static frequency converter's trigger pulse, the harmonic current path of the static frequency converter can be cut off from the physical source before the closing moment, thereby reducing the circulating current hazards and electrical shocks caused by grid-connected operations, and thus enabling safe, accurate, and rapid smooth grid connection in high-frequency start-up scenarios for pumped storage units.

[0057] In one exemplary embodiment, such as Figure 2 As shown, the corresponding speed of the unit is obtained, including:

[0058] S202 obtains the first rotational speed of the unit through physical sensors installed on the unit.

[0059] S204: Based on the unit's operating status, obtain the corresponding voltage information of the unit; based on the voltage information, obtain the corresponding second speed of the unit.

[0060] S206, determine the target speed range in which the first speed is located from the first speed range, the second speed range, and the third speed range; the maximum speed of the first speed range is less than the minimum speed of the second speed range, and the maximum speed range of the second speed range is less than the minimum speed of the third speed range.

[0061] S208, if the target speed range is the first speed range, determine the speed corresponding to the unit based on the first speed; if the target speed range is the second speed range, obtain the first weight and the second weight, and perform weighted processing on the first speed and the second speed based on the first weight and the second weight respectively to obtain the speed corresponding to the unit; if the target speed range is the third speed range, determine the speed corresponding to the unit based on the second speed.

[0062] The first rotational speed refers to the mechanical rotational speed value directly measured and calculated by hardware devices (such as gear discs, photoelectric / magnetoelectric encoders, and other physical sensors) installed on the main shaft of the unit, and belongs to the "hardware measurement value".

[0063] Physical sensors are hardware probes deployed near the rotor of a generator unit. They generate pulse signals by sensing changes in the physical position of the rotor (such as gears cutting magnetic lines of force or blocking light).

[0064] Voltage information refers to the electrical signal characteristics presented at the stator outlet of the generator unit. The core of this information is the frequency of the terminal voltage (i.e., the frequency of the induced electromotive force generated by the rotor rotating and cutting magnetic field lines).

[0065] The second speed refers to the speed value calculated entirely by collecting the voltage information of the unit without relying on physical sensors, and using the inherent mathematical relationship between electrical frequency and mechanical speed (for example, speed = 60 × frequency ÷ number of pole pairs). It belongs to the category of "software observation value".

[0066] The first, second, and third speed ranges are three pre-defined, non-overlapping speed ranges that increase sequentially. For example, 0-5% of the rated speed is the first range, 5%-80% is the second range, and 80%-100% is the third range.

[0067] The first weight and the second weight are the percentage coefficients assigned to the first speed and the second speed respectively within the second speed range (transition section) (the sum of the two is usually 1 or 100%), used to merge the two values ​​into an intermediate value.

[0068] Specifically, the SFC control system simultaneously activates two task threads. On one hand, it receives pulse sequences from physical sensors via the underlying I / O board and calculates the first rotational speed using an internal high-frequency clock, for example, 300 rpm. On the other hand, it acquires the analog voltage waveform from the machine-side PT via the acquisition board, extracts the current voltage frequency through filtering and a phase-locked loop algorithm, and then calculates the second rotational speed, for example, 280 rpm.

[0069] Next, the SFC control system retrieves pre-set threshold ranges from its internal memory. Assume the upper limit of the first range is 300 RPM, the second range is 300-800 RPM, and the lower limit of the third range is 800 RPM. The control system compares the currently acquired first RPM with these thresholds to determine which RPM range the current first RPM falls within.

[0070] If the speed is determined to be in the first speed range, the unit has just started up, the terminal voltage is extremely weak and harmonics are severe, and the second speed may be unreliable. The SFC control system can cut off the data path of the second speed and use the first speed as the final unit speed for subsequent use.

[0071] If the system is determined to be in the second speed range, as the speed increases (assuming the first speed reaches 500 rpm), it enters the transition phase. The SFC control system dynamically looks up a table or calculates the first weight (e.g., 0.4) and the second weight (e.g., 0.6) based on the current speed's specific position within the second range. The control system performs a multiplication-addition operation: final speed = 500 × 0.4 + second speed × 0.6, and outputs this combined value.

[0072] If the speed is determined to be in the third speed range, the unit is close to its rated speed, and the terminal voltage waveform has stabilized. However, physical sensors may have leakage pulses or high-frequency interference due to high speed. The SFC control system can cut off the data path of the first speed and use the second speed as the final unit speed output.

[0073] In this embodiment, by recognizing the physical characteristics of physical sensors—high pulse resolution and strong anti-interference capability at extremely low speeds—and software observations based on voltage information—good waveform quality and no mechanical cumulative error at high speeds—a full-speed-domain segmented adaptive fusion strategy is adopted. This not only avoids the inaccurate observation of weak voltage signals at low speeds but also eliminates measurement noise and delays from hardware sensors at high speeds. Furthermore, weighted processing in the intermediate transition segment enables a seamless and smooth switch from "hardware measurement" to "software observation," eliminating sudden changes in speed feedback that may occur when switching operating conditions from a single speed source. This provides an extremely solid, continuous, and undisturbed speed data foundation for SFC to maintain high-precision torque control across the entire speed domain and for subsequent stable grid connection.

[0074] In some embodiments, such as Figure 3 As shown, adjusting the operating status of the unit based on phase difference and amplitude difference includes the following steps:

[0075] S302 inputs the phase difference to the phase closed-loop controller, calculates the frequency correction amount, and superimposes the frequency correction amount onto the current base output frequency of the static inverter to dynamically adjust the output frequency state of the static inverter so that the phase of the terminal voltage tracks the phase of the grid voltage.

[0076] S304 inputs the amplitude difference to the amplitude closed-loop controller, calculates the excitation current correction amount, and superimposes the excitation current correction amount onto the current base excitation current of the excitation device to dynamically adjust the excitation current state of the unit, so that the amplitude of the generator terminal voltage tracks the amplitude of the grid voltage.

[0077] The phase closed-loop controller and amplitude closed-loop controller are two automatic adjustment algorithms within the SFC control system, such as a PI proportional-integral controller or a PID controller. They can automatically calculate an output quantity that can eliminate the input error value (phase difference or amplitude difference) according to a set mathematical law.

[0078] The frequency correction is a result calculated by the phase closed-loop controller, representing how many hertz the SFC output frequency needs to be "speeded up" or "slowed down" to make up for the lagging phase or catch up with the leading phase.

[0079] The current base output frequency refers to a base frequency value given by the SFC based on the current speed of the unit before entering fine grid-connected regulation. For example, the current speed corresponds to 49.5Hz.

[0080] The excitation current correction is a result calculated by the amplitude closed-loop controller. It represents how many amperes the DC current supplied to the generator rotor needs to be "increased" or "decreased" to change the strength of the magnetic field and thus change the voltage output of the generator stator.

[0081] The current base excitation current is a basic DC current setting value output by the excitation device to maintain the normal operation of the unit before entering fine grid-connected regulation.

[0082] Specifically, after obtaining the calculated "phase difference" (assuming it's +5 degrees, indicating the unit's phase is 5 degrees ahead of the grid), the SFC control system sends this +5 degree to the "phase closed-loop controller." The controller's internal algorithm determines: "It's too far ahead, it needs to slow down." Therefore, it calculates and outputs a "frequency correction amount" (assuming it's -0.05 Hz). The SFC control system then obtains the currently executing "current base output frequency command" (assuming it's 50.0 Hz). The SFC control system calculates the sum of the frequency correction amount and the current base output frequency: 50.0 + (-0.05) = 49.95 Hz. The SFC control system then sends this new 49.95 Hz command to the SFC power unit.

[0083] After receiving the signal, the SFC power unit changes the triggering time of the thyristor, causing the frequency of the current output to the generator to drop to 49.95Hz, thereby "slowing down" the generator and allowing the phase of the generator terminal voltage to gradually return to the grid phase (the phase difference tends to 0).

[0084] For amplitude adjustment, please refer to the following:

[0085] The SFC control system receives the currently calculated "amplitude difference" (assuming it is -500V, indicating that the unit voltage is 500V lower than the grid voltage). This -500V is sent to the "amplitude closed-loop controller". The controller algorithm determines: "The voltage is too low, the magnetic field needs to be increased", and thus outputs an "excitation current correction" (assuming it is +20A).

[0086] The SFC control system acquires the current base excitation current (assumed to be 800A) being executed by the external excitation device. The SFC control system calculates the sum of the current base excitation current and the excitation current correction: 800 + 20 = 820A. The SFC control system sends this new 820A command to the external excitation device via the communication line. Upon receiving the command, the external excitation device increases the DC current supplied to the generator rotor, strengthening the rotor magnetic field. This causes the voltage generated by the stator cutting the magnetic field lines to rise until the generator terminal voltage amplitude equals the grid voltage amplitude (amplitude difference approaches 0).

[0087] In this embodiment, by constructing a dual closed-loop control architecture that decouples phase and amplitude, the complex grid synchronization process is decomposed into two independent adjustment channels that do not interfere with each other: on the one hand, by utilizing the flexible adjustment characteristic of the SFC output frequency, the phase can be quickly and accurately tracked by fine-tuning the frequency; on the other hand, by leveraging the current adjustment capability of the excitation system, the voltage amplitude can be accurately and stably aligned. This not only fundamentally avoids the risks of mutual coupling and oscillation when adjusting a single control variable, but also significantly improves the dynamic response speed and steady-state convergence accuracy of the unit's electrical parameters as they approach the grid parameters.

[0088] In some embodiments, such as Figure 4 As shown, before the control unit reaches the preset speed, the following steps are included:

[0089] S402 If the speed is in the low speed range, the stator current output by the static inverter is obtained, and the amplitude of the stator current is clamped to the preset maximum current threshold.

[0090] S404 If the speed is in the medium speed range, the slope deviation between the speed and the preset acceleration curve is obtained, and the rate of change of the output frequency of the static inverter is adjusted based on the slope deviation.

[0091] S406 If the speed is in the high speed range, obtain the residual between the speed and the preset speed, obtain the adjustment amount corresponding to the output frequency based on the residual, and adjust the output frequency based on the adjustment amount so that the speed converges to the preset speed.

[0092] The low / medium / high speed ranges divide the entire process of the generator unit accelerating from a standstill to its grid-connected speed into three consecutive stages. The low speed range generally refers to the initial startup stage (e.g., 0~20% of rated speed); the medium speed range refers to the steady acceleration stage (e.g., 20%~90%); and the high speed range refers to the stage approaching the grid-connected target speed (e.g., 90%~100%).

[0093] The maximum current threshold is the physical limit of safe current that the SFC and the generator set can withstand. Exceeding this value may cause the thyristors to overheat and be damaged, or damage to the insulation of the generator set's stator windings.

[0094] Slope deviation is the difference between the actual rate of increase in rotational speed (acceleration) and the slope of the pre-planned ideal acceleration curve.

[0095] The rate of change of output frequency is the speed at which the AC frequency output by the SFC to the generator changes. Since frequency directly corresponds to rotational speed, the speed at which the frequency changes determines how fast the generator accelerates.

[0096] The residual is the value in the high-speed range that the current actual speed is still far from the final "preset speed".

[0097] Specifically, in the low-speed range, i.e., the current-limiting safety phase, the static friction is extremely high when the unit first starts up, and there is no back electromotive force at the turbine terminals, making it highly susceptible to current runaway. The SFC control system collects the stator current output by the SFC in real time. The control system internally sets a maximum limit (e.g., a maximum current threshold of 2000A). If the calculated current demand value is greater than 2000A, the control system can forcibly replace it with 2000A. At this time, the SFC outputs constant torque with the maximum allowable current, aiming only to "hard-drive" the unit to operation, without pursuing the speed of acceleration.

[0098] In the mid-speed range, specifically the stage of controlling the slope to maintain stability, the unit is already running, and current is no longer the primary concern. The focus at this point is preventing excessive acceleration that could lead to shaft breakage. The SFC control system calculates the slope of the current speed in real time; for example, if the actual acceleration is 30 revolutions per second. The control system subtracts this from the slope of the "preset acceleration curve" (e.g., the desired acceleration of 25 revolutions per second) to obtain the slope deviation. For example, a slope deviation of +5 revolutions per second² indicates that the unit is rotating too fast. The control system inputs this deviation to the slope controller to generate a command to reduce the "rate of change of output frequency." Upon receiving the command, the SFC power unit slows down the rate of frequency increase, reducing acceleration and operating smoothly along the ideal acceleration curve.

[0099] In the high-speed range, specifically the closed-loop convergence and precision-maintaining stage, the unit is about to reach the preset speed required for grid connection. At this point, it cannot continue to increase at the slope; it must converge the speed precisely. The SFC control system calculates the "residual" (for example, if the target is 500 rpm and the current speed is 495 rpm, the residual is 5 rpm). The control system inputs this residual to the speed closed-loop controller, such as a PID controller, to calculate a small frequency adjustment, such as +0.05Hz. The control system adds this adjustment to the current frequency. As the speed gets closer to 500 rpm, the residual becomes smaller, and the calculated adjustment also becomes smaller. Ultimately, the speed can smoothly and without overshoot "converge" and stabilize at the preset speed of 500 rpm.

[0100] In this embodiment, by clamping the current amplitude at low speeds to strictly safeguard electrical safety, the risk of overcurrent damage caused by the lack of back electromotive force during the zero-start phase can be completely avoided. In the mid-speed range, the control focus is switched from current limiting to frequency change rate adjustment based on slope deviation, which can effectively suppress shaft torsional vibration and mechanical stress impact induced by excessive acceleration. In the high-speed range, the closed-loop convergence control based on residuals is seamlessly integrated, which can achieve precise stopping at the target speed without overshoot. This segmented mechanism can ensure the smoothness of the start-up process and the accuracy of speed control while maximizing equipment safety and mechanical life.

[0101] In some embodiments, the grid frequency can also be considered to ensure the accuracy of grid connection timing. That is, after the control unit reaches the preset speed, the generator terminal phase, generator terminal amplitude, and generator terminal frequency are obtained based on the generator operating state, and the grid phase, grid amplitude, and grid frequency are obtained based on the grid operating state; the phase difference between the generator terminal phase and the grid phase, the amplitude difference between the generator terminal amplitude and the grid amplitude, and the frequency difference between the generator terminal frequency and the grid frequency are obtained; the operating state of the generator is adjusted based on the phase difference, amplitude difference, and frequency difference; when the phase difference, amplitude difference, and frequency difference corresponding to the adjusted operating state meet the preset conditions, after blocking the trigger pulse of the static inverter, a grid connection command is issued so that the external device responds to the grid connection command to connect the generator to the grid.

[0102] Specifically, when the SFC control system determines that the unit speed has been dragged to the preset speed, it immediately switches the control mode. It uses a high-speed acquisition channel to capture the voltage waveforms of the unit's power supply (PT) and the grid's power supply (PT) in real time, and uses algorithms (such as a phase-locked loop or FFT) to extract the phase, amplitude, and frequency at the generator end, as well as the phase, amplitude, and frequency of the grid. Then, it performs simple subtraction operations in memory to calculate the phase difference, amplitude difference, and frequency difference in real time.

[0103] The SFC control system sends the calculated three differences to their respective closed-loop controllers:

[0104] Regarding frequency difference: The SFC control system calculates the frequency correction amount and fine-tunes the frequency command sent to the SFC power cabinet to bring the unit's speed closer to the grid frequency.

[0105] Regarding the amplitude difference: The SFC control system calculates the excitation correction amount and sends it to the excitation system through the communication line, so that the excitation system adjusts the rotor current, thereby changing the magnitude of the generator terminal voltage to make it equal to the grid voltage.

[0106] Regarding phase difference: Similarly, the output frequency is finely adjusted by SFC to align the generator waveform and the grid waveform in terms of angle.

[0107] The above steps can be repeated until the three differences become smaller and smaller.

[0108] The SFC control system constantly monitors these three differences. When it detects that at a certain moment, the phase difference, amplitude difference, and frequency difference all fall within the preset dead zone, the SFC control system can immediately send a blocking trigger pulse command to the SFC power cabinet via the digital I / O port. The SFC power cabinet stops working, and the unit loses its external driving force. However, since it is already synchronized with the grid, the unit will maintain synchronous operation on its own, and the SFC current decays instantaneously, so it will not interfere with grid connection.

[0109] After confirming that the pulse has been blocked (typically with a delay of tens of milliseconds to ensure zero current), the SFC control system sends a "grid connection command" to the outside world via hardwiring or a communication network. The closing coil inside the external device (circuit breaker GCB) receives this command and generates a strong magnetic force to pull the mechanical contacts closed. At this point, the unit is physically connected to the grid, and the grid connection process is complete.

[0110] In this embodiment, by constructing a three-dimensional closed-loop adjustment mechanism for phase, amplitude, and frequency, it is possible to ensure that the electrical characteristics of the unit are precisely aligned with the power grid at the moment of grid connection, thereby fundamentally eliminating the huge transient inrush current and electromagnetic torque mutation caused by parameter mismatch during grid connection.

[0111] In some embodiments, such as Figure 5 As shown, when the phase difference and amplitude difference corresponding to the adjusted operating state meet the preset conditions, a grid connection command is issued after blocking the trigger pulse of the static inverter, including:

[0112] S502, obtains the inherent mechanical closing time of the external device, and the extinction time required for the current to decay to zero after the static inverter executes the blocking trigger pulse action.

[0113] S504 sums the mechanical closing time and the closing time to obtain the comprehensive lead time.

[0114] S506 converts the integrated lead time into the corresponding target lead phase angle based on the frequency difference between the generating unit and the power grid.

[0115] S508, when the phase difference monitored in real time decays to the point where it is equal to the target leading phase angle, executes the action of blocking the trigger pulse of the static inverter, and issues a grid connection command after the extinction time.

[0116] The inherent mechanical closing time is the time elapsed from when the external circuit breaker (a large mechanical switch) receives the command to energize the closing coil to when the internal three-phase moving contacts are fully closed. This is a purely mechanical delay, typically a fixed value (e.g., 50 to 80 milliseconds).

[0117] The extinction time is the period after the SFC receives the "block trigger pulse" command. Due to the huge inductance in the main circuit, the current will not become zero instantly, but will gradually decay to zero. This period is called the extinction time.

[0118] The overall lead time is the absolute time required from the control system making the decision to "issue the grid connection command" to the final closing of the circuit breaker and the absence of any residual SFC current interference in the circuit. It is the sum of the mechanical closing time and the extinguishing time.

[0119] The target lead phase angle is because during the integrated lead time, the unit's phase continues to move forward (relative to the grid). In order to offset the phase shift caused by this "walking time", the control system must pull the trigger at a specific angle (this angle is the target lead phase angle) before the phase difference reaches 0 degrees.

[0120] Specifically, the SFC control system retrieves the pre-stored "inherent mechanical closing time" of the external circuit breaker from its internal database, assuming it is 60ms, and estimates or looks up the "extinguishing time" after the SFC blocking pulse under the current operating condition in real time, assuming it is 10ms.

[0121] Next, the SFC control system adds the two together to obtain a combined lead time of 70ms. In other words, if you want to close the switch at time T0, you need to issue the grid connection command at time T0 minus 70ms.

[0122] Subsequently, the SFC control system acquires the real-time frequency difference between the generating unit and the grid. Assuming the generating unit's frequency is 0.1 Hz higher than the grid frequency, meaning the unit is running faster, the system calculates how many degrees the phase advances per millisecond. Then, the comprehensive lead time (70 ms) is substituted into the calculation: Target lead phase angle = angular velocity × 70 ms. Assuming the calculation shows that within these 70 ms, the generating unit will lead the grid by 2.52 degrees.

[0123] The SFC control system continuously monitors the real-time "phase difference". When it detects that the phase difference is gradually decreasing from a large value to exactly 2.52 degrees, it immediately performs two operations: First, it instantly sends a "block trigger pulse" command to the SFC power cabinet; second, it starts an internal precise timer to count down the "extend time (10ms)" that was just calculated.

[0124] Finally, when the 10ms timer reaches zero (at which point the SFC current is safely at zero), the SFC control system sends a "grid connection command" to the external device. After another 60ms mechanical action, the circuit breaker closes, at which point the phase difference is perfectly close to 0 degrees.

[0125] In this embodiment, by jointly modeling the inherent mechanical action delay of the circuit breaker and the electrical delay of the current decay inside the SFC, the comprehensive lead time is derived and accurately converted into a dynamic target lead phase angle as a trigger reference. This can eliminate the closing phase angle lag or lead error caused by the time difference between the "command time" and the "physical closing time" in traditional grid-connected control. Without increasing any hardware cost, it can achieve ultimate compensation for the inherent delay and reduce the phase impact at the moment of grid connection to the theoretical minimum.

[0126] In some embodiments, such as Figure 6 As shown, the following steps can also be performed when adjusting the output frequency:

[0127] S602, obtain the absolute value of the frequency difference between the terminal frequency and the grid frequency, and the phase difference change rate over time.

[0128] S604, determine whether the absolute value of the frequency difference is greater than the preset power grid disturbance threshold.

[0129] S606 If the disturbance exceeds the grid disturbance threshold, the proportional gain of the phase closed-loop controller is increased based on the phase difference change rate, and the integral time constant is shortened.

[0130] S608 calculates the frequency correction amount based on the adjusted proportional gain and integral time constant, and adjusts the output frequency of the static inverter based on the frequency correction amount.

[0131] The absolute value of the frequency difference is the absolute value of the difference between the current frequency of the generating unit and the grid frequency. The phase difference change rate characterizes how quickly the phase difference changes over time, reflecting the rate at which the phase error is being widened or narrowed. The grid disturbance threshold is a pre-set frequency difference boundary value (e.g., 0.05Hz) used to distinguish whether the current power grid is in an "extremely stable state" or in a "dynamic frequency fluctuation state caused by the access of new energy sources such as wind power / solar power".

[0132] The proportional gain (P) and integral time constant (I) are two core parameters in a PID closed-loop controller. The proportional gain determines the response speed, i.e., how aggressively the system works after detecting an error. The integral time constant determines the "accumulation speed" of the system in eliminating steady-state errors (the shorter the time, the faster the error is eliminated).

[0133] Specifically, during the adjustment of the unit's operating status, the SFC control system calculates the phase difference while simultaneously calculating two characteristic values ​​in real time in the background: the current absolute value of the frequency difference and the current rate of change of the phase difference. The SFC control system compares the absolute value of the frequency difference with an internally set grid disturbance threshold. If the absolute value of the frequency difference is determined to be greater than the threshold, it indicates that the grid frequency is experiencing severe dynamic fluctuations.

[0134] Once a grid fluctuation condition is confirmed, the SFC control system can determine the parameter adjustment amount based on the phase difference change rate. Based on this adjustment, the proportional gain of the phase closed-loop controller is dynamically increased to improve the system's dynamic response speed to phase errors. Simultaneously, the integral time constant is decreased to accelerate the elimination of steady-state errors. Then, the frequency correction amount is calculated based on the adjusted proportional gain and integral time constant. Finally, the output frequency is determined based on this frequency correction amount, and the unit's operating state is adjusted accordingly.

[0135] In this embodiment, by real-time detection of frequency difference and phase difference change rate, the dynamic disturbance conditions under the background of large power grid are accurately identified, and a dynamic adaptive adjustment mechanism of PI parameter based on disturbance intensity is introduced, so that when the power grid frequency fluctuates drastically, the control system can instantly switch from "stable tracking mode" to "strong anti-disturbance mode", thereby effectively avoiding the loss of synchronization or oscillation between the unit phase and the power grid phase caused by the controller response lag, and greatly improving the grid connection robustness of SFC driven units in dealing with complex and harsh power grid environments.

[0136] In one exemplary embodiment, pumped storage power stations are key facilities for building new power systems and supporting the high-proportion consumption of new energy sources. To meet the new trends in power station operation, it is necessary to ensure the response speed, reliability, and control accuracy of pumped storage units during startup. Static frequency converters (SFDs) are the core equipment for starting pumped storage units under pumping conditions. To ensure synchronization efficiency and improve grid connection efficiency, a synchronization function can be set in the control system applied to the SFD.

[0137] In this embodiment, all functional modules, including speed observation, phase closed-loop control, amplitude closed-loop control, and intelligent grid connection decision-making, are integrated into the control system of the static inverter. The system collects the unit's operating status and grid parameters in real time, completes the entire startup and synchronization process through internal algorithms, and finally automatically completes grid connection when the conditions are met.

[0138] Specifically, the control system includes a speed observation module, a phase detection and closed-loop control module, an amplitude detection and closed-loop control module, and an intelligent decision-making module. The speed observation module employs multi-source information fusion technology to accurately acquire and track the unit's rotational speed in real time. The phase detection and closed-loop control module calculates the phase difference between the grid voltage and the generator terminal voltage in real time and eliminates this difference through a closed-loop algorithm. The amplitude detection and closed-loop control module calculates the amplitude difference between the grid voltage and the generator terminal voltage in real time and gradually approximates the grid voltage amplitude through closed-loop adjustment. The intelligent decision-making module comprehensively assesses synchronization conditions and directs the execution of pulse blocking and grid connection operations.

[0139] refer to Figure 7The system collects real-time data on grid operating status and generator unit operating status through grid voltage detection unit, output voltage detection unit, output current detection unit, excitation current detection unit, and motor parameters. The collected signals are then fed into a signal processing and fusion module for filtering, conditioning, and data fusion—a preprocessing step—to ensure the reliability of subsequent data.

[0140] Next, the speed observation and closed-loop control module, based on the fused motor parameters and electrical signal information, accurately observes the unit speed and outputs control commands to accelerate the unit according to a predetermined curve. That is, it controls the unit to accelerate to a preset speed based on the predetermined curve.

[0141] After reaching the preset speed, the phase / amplitude detection and closed-loop control module calculates the phase difference and amplitude difference in real time, and outputs the correction amount through the closed-loop controller (such as an adaptive PID controller) to dynamically adjust the output of the SFC and excitation device, so that the phase and amplitude of the generator terminal voltage accurately track the grid voltage.

[0142] refer to Figure 8 The intelligent decision-making and logic control module continuously monitors the phase difference, amplitude difference, and frequency difference. When all differences are less than the preset threshold, it is determined that the grid connection conditions are met. Then, the "pulse blocking and protection logic" is first triggered to block the trigger pulse of the SFC, and then the grid connection control and execution module sends a closing command to the circuit breaker to complete the grid connection.

[0143] In addition, the system may include a status monitoring and display module to support human-computer interaction.

[0144] In this embodiment, by integrating the automatic synchronization function into the SFC, a separate external synchronization device is eliminated. This not only reduces equipment procurement costs but also simplifies system wiring, debugging, and maintenance, improving economic efficiency. Furthermore, the integrated control architecture reduces inter-system communication latency, significantly shortening the process from meeting synchronization conditions to issuing grid connection commands. This aligns with the new power system's focus on rapid response to grid peak shaving and frequency regulation requirements for pumped storage power stations and also helps improve the grid's capacity to absorb new energy sources. In addition, internal high-precision phase and amplitude closed-loop control enables more accurate synchronization, effectively reducing grid connection inrush current and contributing to the safe and stable operation of the main equipment. Finally, high integration reduces external dependencies and the number of interfaces, lowering the probability of failure and thus improving the automation level and reliability of the entire startup process.

[0145] It should be understood that although the steps in the flowcharts of the above embodiments are shown sequentially according to the arrows, these steps are not necessarily executed in the order indicated by the arrows. Unless explicitly stated herein, there is no strict order restriction on the execution of these steps, and they can be executed in other orders. Moreover, at least some steps in the flowcharts of the above embodiments may include multiple steps or multiple stages. These steps or stages are not necessarily completed at the same time, but can be executed at different times. The execution order of these steps or stages is not necessarily sequential, but can be performed alternately or in turn with other steps or at least some of the steps or stages of other steps.

[0146] Based on the same inventive concept, this application also provides a grid-connected control device for a static frequency converter (SFD) for implementing the grid-connected control method for an SFD described above. The solution provided by this device is similar to the solution described in the above method. Therefore, the specific limitations of one or more embodiments of the grid-connected control device for an SFD provided below can be found in the limitations of the grid-connected control method for an SFD described above, and will not be repeated here.

[0147] In one exemplary embodiment, such as Figure 9 As shown, a grid-connected control system 900 for a static frequency converter is provided, including: a signal detection module 901, a speed observation module 902, a control module 903, and a grid-connected module 904, wherein:

[0148] Signal detection module 901 is used to acquire the power grid operating status and the unit operating status;

[0149] The speed observation module 902 is used to obtain the unit operating status from the signal detection module and obtain the corresponding speed of the unit based on the unit operating status;

[0150] The control module 903 is used to acquire the rotational speed measured by the speed observation module. After the rotational speed of the control unit reaches the preset speed, it obtains the generator terminal phase and generator terminal amplitude based on the unit operating status obtained from the signal detection module, and obtains the grid phase and grid amplitude based on the grid operating status obtained from the signal detection module. It acquires the phase difference between the generator terminal phase and the grid phase, and the amplitude difference between the generator terminal amplitude and the grid amplitude. Based on the phase difference and amplitude difference, it adjusts the unit operating status so that when the phase difference and amplitude difference of the adjusted operating status meet the preset conditions, it issues the first grid connection command.

[0151] The grid connection module 904 is used to block the trigger pulse of the static inverter in response to the first grid connection command, and then issue a second grid connection command so that the external device responds to the second grid connection command to connect the unit to the power grid.

[0152] In some embodiments, in obtaining the rotational speed of the generator set, the speed observation module 902 is specifically used to: obtain the first rotational speed of the generator set through physical sensors installed on the generator set; obtain the voltage information of the generator set based on the operating status of the generator set; obtain the second rotational speed of the generator set based on the voltage information; determine the target rotational speed range in which the first rotational speed is located from the first rotational speed range, the second rotational speed range, and the third rotational speed range; the maximum rotational speed of the first rotational speed range is less than the minimum rotational speed of the second rotational speed range, and the maximum rotational speed range of the second rotational speed range is less than the minimum rotational speed of the third rotational speed range; if the target rotational speed range is the first rotational speed range, determine the rotational speed of the generator set based on the first rotational speed; if the target rotational speed range is the second rotational speed range, obtain the first weight and the second weight, and perform weighted processing on the first rotational speed and the second rotational speed based on the first weight and the second weight respectively to obtain the rotational speed of the generator set; if the target rotational speed range is the third rotational speed range, determine the rotational speed of the generator set based on the second rotational speed.

[0153] In some embodiments, regarding adjusting the operating state of the unit based on phase difference and amplitude difference, the control module 903 is specifically used to: input the phase difference to the phase closed-loop controller, calculate the frequency correction amount, and superimpose the frequency correction amount onto the current base output frequency of the static inverter to dynamically adjust the output frequency state of the static inverter so that the phase of the generator terminal voltage tracks the phase of the grid voltage; input the amplitude difference to the amplitude closed-loop controller, calculate the excitation current correction amount, and superimpose the excitation current correction amount onto the current base excitation current of the excitation device to dynamically adjust the excitation current state of the unit so that the amplitude of the generator terminal voltage tracks the amplitude of the grid voltage.

[0154] In some embodiments, regarding the control unit's corresponding speed reaching a preset speed, the control module 903 is specifically configured to: if the speed is in the low speed range, acquire the stator current output by the static inverter and control the amplitude of the stator current to be clamped to a preset maximum current threshold; if the speed is in the medium speed range, acquire the slope deviation between the speed and a preset acceleration curve, and adjust the rate of change of the output frequency of the static inverter based on the slope deviation; if the speed is in the high speed range, acquire the residual between the speed and the preset speed, obtain the adjustment amount corresponding to the output frequency based on the residual, and adjust the output frequency based on the adjustment amount so that the speed converges to the preset speed.

[0155] In some embodiments, when the phase difference and amplitude difference corresponding to the adjusted operating state meet preset conditions, the grid connection module 904 is specifically used to: obtain the inherent mechanical closing time of the external device and the extinction time required for the current to decay to zero after the static inverter executes the action of blocking the trigger pulse; sum the mechanical closing time and the extinction time to obtain the comprehensive lead time; convert the comprehensive lead time into the corresponding target lead phase angle based on the frequency difference between the unit and the grid; when the phase difference monitored in real time decays to be equal to the target lead phase angle, execute the action of blocking the trigger pulse of the static inverter, and issue the grid connection command after the extinction time has elapsed.

[0156] In some embodiments, the control module 903 is further configured to: acquire the absolute value of the frequency difference between the generator frequency and the grid frequency, and the phase difference change rate over time; determine whether the absolute value of the frequency difference is greater than a preset grid disturbance threshold; if it is greater than the grid disturbance threshold, increase the proportional gain of the phase closed-loop controller based on the phase difference change rate and shorten the integral time constant; calculate the frequency correction amount based on the adjusted proportional gain and integral time constant, and adjust the output frequency of the static inverter based on the frequency correction amount.

[0157] The modules in the grid-connected control system applied to static frequency converters described above can be implemented entirely or partially through software, hardware, or a combination thereof. These modules can be embedded in or independent of the processor in a computer device, or stored in the memory of a computer device as software, so that the processor can call and execute the corresponding operations of each module.

[0158] In one exemplary embodiment, a computer device is provided, which may be a terminal, and its internal structure diagram may be as follows: Figure 10As shown, the computer device includes a processor, memory, input / output interface, communication interface, display unit, and input device. The processor, memory, and input / output interface are connected via a system bus, and the communication interface, display unit, and input device are also connected to the system bus via the input / output interface. The processor provides computing and control capabilities. The memory includes non-volatile storage media and internal memory. The non-volatile storage media stores the operating system and computer programs. The internal memory provides an environment for the operation of the operating system and computer programs in the non-volatile storage media. The input / output interface is used for exchanging information between the processor and external devices. The communication interface is used for wired or wireless communication with external terminals; wireless communication can be achieved through Wi-Fi, mobile cellular networks, Near Field Communication (NFC), or other technologies. When the computer program is executed by the processor, it implements a grid-connected control method for a static frequency inverter. The display unit is used to form a visually visible image and can be a display screen, projection device, or virtual reality imaging device. The display screen can be an LCD screen or an e-ink screen. The input device of the computer device can be a touch layer covering the display screen, or buttons, trackballs, or touchpads set on the casing of the computer device, or external keyboards, touchpads, or mice, etc.

[0159] Those skilled in the art will understand that Figure 10 The structure shown is merely a block diagram of a portion of the structure related to the present application and does not constitute a limitation on the computer device to which the present application is applied. Specific computer devices may include more or fewer components than those shown in the figure, or combine certain components, or have different component arrangements.

[0160] In one exemplary embodiment, a computer device is provided, including a memory and a processor, wherein the memory stores a computer program, and the processor executes the computer program to implement the steps in the above-described method embodiments.

[0161] In one embodiment, a computer-readable storage medium is provided having a computer program stored thereon, which, when executed by a processor, implements the steps in the above method embodiments.

[0162] In one embodiment, a computer program product is provided, including a computer program that, when executed by a processor, implements the steps in the above method embodiments.

[0163] Those skilled in the art will understand that all or part of the processes in the methods of the above embodiments can be implemented by a computer program instructing related hardware. The computer program can be stored in a non-volatile computer-readable storage medium, and when executed, it can include the processes of the embodiments of the above methods. Any references to memory, databases, or other media used in the embodiments provided in this application can include at least one of non-volatile memory and volatile memory. Non-volatile memory can include read-only memory (ROM), magnetic tape, floppy disk, flash memory, optical memory, high-density embedded non-volatile memory, resistive random access memory (ReRAM), magnetic random access memory (MRAM), ferroelectric random access memory (FRAM), phase change memory (PCM), graphene memory, etc. Volatile memory can include random access memory (RAM) or external cache memory, etc. By way of illustration and not limitation, RAM can take many forms, such as Static Random Access Memory (SRAM) or Dynamic Random Access Memory (DRAM). The databases involved in the embodiments provided in this application may include at least one type of relational database and non-relational database. Non-relational databases may include, but are not limited to, blockchain-based distributed databases. The processors involved in the embodiments provided in this application may be general-purpose processors, central processing units, graphics processing units, digital signal processors, programmable logic devices, quantum computing-based data processing logic devices, artificial intelligence (AI) processors, etc., and are not limited to these.

[0164] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this application.

[0165] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of this patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this application should be determined by the appended claims.

Claims

1. A grid-connected control method for a static frequency converter, characterized in that, The method includes: Obtain the power grid operating status and generator operating status; obtain the corresponding speed of the generator; After controlling the rotational speed of the generator unit to reach the preset rotational speed, the generator terminal phase and generator terminal amplitude are obtained based on the generator unit's operating state, and the grid phase and grid amplitude are obtained based on the grid's operating state. The phase difference between the generator terminal phase and the grid phase, and the amplitude difference between the generator terminal amplitude and the grid amplitude are obtained; the operating state of the generator unit is adjusted based on the phase difference and the amplitude difference. When the phase difference and amplitude difference corresponding to the adjusted operating state meet the preset conditions, after blocking the trigger pulse of the static inverter, a grid connection command is issued so that the external device responds to the grid connection command to connect the unit into the power grid.

2. The method according to claim 1, characterized in that, The process of obtaining the rotational speed of the generator unit includes: The first rotational speed of the unit is obtained by physical sensors installed on the unit. Based on the unit's operating status, obtain the voltage information corresponding to the unit; based on the voltage information, obtain the second rotational speed corresponding to the unit. The target speed range in which the first speed is located is determined from the first speed range, the second speed range, and the third speed range; the maximum speed of the first speed range is less than the minimum speed of the second speed range, and the maximum speed range of the second speed range is less than the minimum speed of the third speed range; If the target speed range is the first speed range, the speed corresponding to the unit is determined based on the first speed. If the target speed range is the second speed range, obtain the first weight and the second weight, and perform weighted processing on the first speed and the second speed based on the first weight and the second weight respectively to obtain the speed corresponding to the unit; If the target speed range is the third speed range, the speed corresponding to the unit is determined based on the second speed.

3. The method according to claim 1, characterized in that, The adjustment of the unit's operating state based on the phase difference and the amplitude difference includes: The phase difference is input to the phase closed-loop controller to calculate the frequency correction amount. The frequency correction amount is then superimposed on the current base output frequency of the static inverter to dynamically adjust the output frequency state of the static inverter, so that the phase of the terminal voltage tracks the phase of the grid voltage. The amplitude difference is input to the amplitude closed-loop controller to calculate the excitation current correction amount. The excitation current correction amount is then superimposed on the current base excitation current of the excitation device to dynamically adjust the excitation current state of the unit, so that the amplitude of the generator terminal voltage tracks the amplitude of the grid voltage.

4. The method according to claim 1, characterized in that, Before the speed corresponding to the unit reaches the preset speed, the following steps are included: If the speed is in the low speed range, the stator current output by the static inverter is obtained, and the amplitude of the stator current is clamped to a preset maximum current threshold. If the speed is in the medium speed range, the slope deviation between the speed and the preset acceleration curve is obtained, and the rate of change of the output frequency of the static inverter is adjusted based on the slope deviation. If the rotational speed is in the high rotational speed range, the residual between the rotational speed and the preset rotational speed is obtained, and the adjustment amount corresponding to the output frequency is obtained based on the residual. The output frequency is adjusted based on the adjustment amount so that the rotational speed converges to the preset rotational speed.

5. The method according to claim 1, characterized in that, When the phase difference and amplitude difference corresponding to the adjusted operating state meet the preset conditions, after blocking the trigger pulse of the static inverter, a grid connection command is issued, including: The inherent mechanical closing time of the external device and the extinction time required for the current to decay to zero after the static inverter executes the blocking trigger pulse action are obtained; The combined lead time is obtained by summing the mechanical closing time and the closing time. Based on the frequency difference between the generating unit and the power grid, the integrated lead time is converted into the corresponding target lead phase angle; When the phase difference monitored in real time decays to the point where it is equal to the target lead phase angle, the action of blocking the trigger pulse of the static inverter is executed, and the grid connection command is issued after the extinction time has elapsed.

6. The method according to claim 1, characterized in that, The method further includes: Obtain the absolute value of the frequency difference between the terminal frequency and the grid frequency, and the rate of change of the phase difference over time; Determine whether the absolute value of the frequency difference is greater than a preset power grid disturbance threshold; If the disturbance exceeds the grid disturbance threshold, the proportional gain of the phase closed-loop controller is increased based on the phase difference change rate, and the integral time constant is shortened. The frequency correction is calculated based on the adjusted proportional gain and integral time constant, and the output frequency of the static inverter is adjusted based on the frequency correction.

7. A grid-connected control system for a static frequency converter, characterized in that, The system includes: The signal detection module is used to acquire the power grid operating status and the unit operating status; The speed observation module is used to obtain the unit's operating status from the signal detection module and obtain the corresponding rotational speed of the unit; The control module is used to acquire the rotational speed measured by the speed observation module, and after controlling the rotational speed of the unit to reach a preset rotational speed, obtain the generator terminal phase and generator terminal amplitude of the unit based on the unit operating status acquired from the signal detection module, and obtain the grid phase and grid amplitude of the grid based on the grid operating status acquired from the signal detection module; acquire the phase difference between the generator terminal phase and the grid phase, and the amplitude difference between the generator terminal amplitude and the grid amplitude; adjust the operating status of the unit based on the phase difference and the amplitude difference, so that when the phase difference and amplitude difference of the adjusted operating status meet preset conditions, a first grid connection command is issued; The grid connection module is used to block the trigger pulse of the static inverter in response to the first grid connection command, and then issue a second grid connection command so that the external device responds to the second grid connection command to connect the unit to the power grid.

8. A computer device comprising a memory and a processor, wherein the memory stores a computer program, characterized in that, When the processor executes the computer program, it implements the steps of the method according to any one of claims 1 to 6.

9. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by a processor, it implements the steps of the method according to any one of claims 1 to 6.

10. A computer program product, comprising a computer program, characterized in that, When the computer program is executed by a processor, it implements the steps of the method according to any one of claims 1 to 6.

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