A phase control strategy for improving transient stability of virtual synchronous new energy units

Abstract

The present application relates to the technical field of data processing, and provides a phase control strategy for improving transient stability of a virtual synchronous new energy unit, which realizes tracking of the voltage phase of the potential phase during a fault period, maintains a constant phase difference and effectively prevents power angle divergence by a series of steps such as fault detection, phase locking, phase control and frequency locking, fault clearing detection and recovery of normal operation, etc., while locking the frequency at the grid frequency to ensure that the system can smoothly switch back to the traditional control strategy after the fault is cleared. This strategy effectively deals with the system instability problem caused by excessive phase jump at the moment of fault, significantly improves the transient stability of the virtual synchronous new energy unit, and provides a strong guarantee for the safe and stable operation of the power system.

Description

Technical Field

[0001] This invention relates to the field of data processing technology, and in particular to a phase control strategy for improving the transient stability of virtual synchronous renewable energy units. Background Technology

[0002] In recent years, with changes in the global energy structure, the proportion of new energy power generation has been increasing year by year, while the proportion of traditional synchronous generators has been declining. Due to the randomness, volatility, and intermittency of new energy sources, the inertia and damping of the system are constantly decreasing. This means that during transient processes after large disturbances such as load shedding, the overcurrent caused by the voltage drop in the grid can damage power electronic devices. The system also has a larger rate of frequency change and a wider frequency range, resulting in poorer transient stability, which seriously threatens the safety of the power system.

[0003] To improve the transient stability of renewable energy sources after grid connection, domestic and international scholars have simulated the characteristics of synchronous generators and proposed virtual synchronous machine technology. This technology enables inverters to possess damping, inertia characteristics, and voltage and frequency output characteristics similar to synchronous generators, thereby improving the system's transient performance. Under virtual synchronous control, the power, inertia, frequency, and phase of renewable energy sources are artificially constructed and can be rapidly controlled, providing multiple possible approaches to enhance the transient stability of virtual synchronous renewable energy sources during faults. Some studies have focused on the power angle characteristics based on virtual synchronous machines (…). Figure 1 This paper analyzes and proposes a transient control strategy for a virtual synchronous machine that adaptively adjusts the active power deviation. An adaptive coefficient is introduced to quickly adjust the reference value of active power during faults, improving transient characteristics. However, it does not consider the phase jump at the moment of fault. In reality, at the moment of fault occurrence, due to the connection of the ground loop, the circuit topology changes abruptly, and the phase of the external equivalent voltage jumps. If the initial operating point of the power angle jumps to the unstable operating region, under the traditional control strategy of the virtual synchronous machine, the active power reference value in the unstable operating region is always greater than the output active power. This active power difference leads to an increase in frequency and forms positive feedback, ultimately resulting in instability. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a phase control strategy to improve the transient stability of virtual synchronous renewable energy units. Specifically, for phase jumps during fault events, this patent designs a method to lock the internal potential after a fault. and terminal voltage A phase control strategy based on the phase difference between the two phases is proposed. During a fault, the internal potential phase is no longer generated by frequency integration, but instead tracks the terminal voltage phase, maintaining the phase difference between them at the instant of the fault to prevent power angle divergence. After the fault, the system switches back to a virtual synchronous conventional control strategy. To achieve a smooth switch, the control frequency is locked to the grid frequency during the fault. The proposed strategy can cope with instability caused by excessive phase jumps at the instant of a fault.

[0005] To solve the above-mentioned technical problems, the specific technical solution of the present invention is as follows:

[0006] This invention provides a phase control strategy for improving the transient stability of virtual synchronous renewable energy units, comprising:

[0007] S101: Fault detection steps: acquire system data, utilize fault detection on the acquired data, and measure the common point voltage U in real time. PCC Amplitude, monitoring whether the system malfunctions, if U PCC If the value is less than 0.9pu, the system is considered to have a fault, and the fault signal changes from low level to high level after a rising edge.

[0008] S102: Phase-locking step. When the system detects a fault, the phase-locking circuit locks the phase of the internal potential and terminal voltage at the instant of the fault. The fault signal generated by the fault detection circuit is introduced, and the trigger is activated by the rising edge of the fault signal changing from 0 to 1, locking the phase θ of the internal potential at this moment. E and terminal voltage phase θ U Calculate and lock the difference δ0 between the two;

[0009] S103: Phase control and frequency locking steps, during system faults, utilize the phase calculation stage to calculate the terminal voltage phase θ in real time. U And lock the internal potential phase at θ U +δ0, and control the frequency separately, locking the frequency to the grid frequency ω. g ;

[0010] S104: Fault clearing detection step. Continue to use fault detection to determine whether the fault has been cleared. If the fault has been cleared, prepare to switch back to the traditional control strategy; otherwise, continue to execute the phase control and frequency locking steps.

[0011] S105: Normal operation restoration procedure. After the fault is cleared, a virtual internal potential phase is generated based on the virtual synchronization control link, the forced locking phase is canceled, the system switches back to the traditional control strategy, normal operation is restored, the voltage rises, the fault signal changes from high level to low level after a falling edge, and the system returns to the operating state before the fault.

[0012] Furthermore, the phase control strategy for improving the transient stability of virtual synchronous renewable energy units described in this invention, step S101 includes:

[0013] The common point voltage U is measured in real time using the fault detection process. PCC The amplitude;

[0014] The system is being monitored for faults, specifically based on the common point voltage U.PCC Is the amplitude less than 0.9 pu?

[0015] If U PCC If the amplitude is less than 0.9 pu, the system is considered to have malfunctioned;

[0016] If the fault signal changes from low level to high level after a rising edge, then a system fault has occurred.

[0017] Furthermore, in the phase control strategy for improving the transient stability of virtual synchronous renewable energy units described in this invention, step S102 includes:

[0018] By measuring the common point voltage U in real time PCC The amplitude is used to monitor whether a fault has occurred in the current system. If U PCC If the amplitude is less than 0.9pu, the system is considered to have a fault, and the fault signal changes from low level to high level after a rising edge;

[0019] When the fault signal changes from 0 to 1 on a rising edge, the phase-locked loop is activated to lock the internal potential (θ) at the moment of the fault. E ) and terminal voltage (θ) U The phase of )

[0020] Simultaneously with triggering phase locking, the phase difference δ0 between the internal potential and the terminal voltage is calculated. This is achieved by locking the θ at the instant of the fault. E and θ U This is achieved by the phase difference δ0 being the difference between the two.

[0021] During a fault, the phase of the internal potential is locked to the phase of the terminal voltage plus a phase difference δ0, i.e., θ. E =θ U +δ0.

[0022] Furthermore, in the phase control strategy for improving the transient stability of virtual synchronous renewable energy units described in this invention, step S103 includes:

[0023] Real-time measurement of common point voltage U PCC The amplitude, if U PCC If the amplitude is less than 0.9 pu, the system is considered to have malfunctioned;

[0024] The fault signal changes from low to high via a rising edge. A trigger is used to lock the phase of the internal potential and terminal voltage at the instant of the fault. The trigger is activated by the rising edge of the fault signal changing from 0 to 1, locking the phase θ of the internal potential at that moment. E and terminal voltage phase θ U The phase difference δ0 between the two is calculated.

[0025] The direct-axis and quadrature-axis components of the terminal voltage are extracted in real time, and the current terminal voltage phase θ is calculated using a preset formula. U The final terminal voltage phase is obtained after low-pass filtering.

[0026] Lock the internal potential phase at θ U If +δ0, then the phase is stable during the fault period;

[0027] Lock the frequency to the grid frequency ω g This is used to avoid frequency shift after fault clearance;

[0028] The fault detection is used to determine whether the fault has been cleared. If the fault has been cleared, the locked phase is released, the system switches back to the traditional virtual synchronous control strategy, the voltage rises, the fault signal goes low, and the system recovers.

[0029] Furthermore, in the phase control strategy for improving the transient stability of virtual synchronous renewable energy units described in this invention, step S104 includes:

[0030] After a system failure occurs, the fault detection process will generate a fault signal;

[0031] To determine whether the fault has been cleared, the common point voltage U is measured in real time through the fault detection process. PCC The amplitude;

[0032] If the common point voltage U PCC If the amplitude recovers to above the set threshold, the fault is considered to have been cleared.

[0033] At this point, the fault signal changes from high level to low level after a falling edge, indicating that the fault has been eliminated.

[0034] The system triggers a control strategy switch. When the fault signal is detected to go low, the system confirms that the fault has been cleared. After confirming that the fault has been cleared, the system triggers the control strategy switch mechanism to switch back from the phase control strategy to the virtual synchronous traditional control strategy.

[0035] After switching back to the traditional control strategy, the system will regenerate the virtual internal potential phase based on the virtual synchronization control link, lock the frequency to the grid frequency, and the output active power will quickly converge to the active power reference value. The system will then return to the stable operating state before the fault, achieving transient stability.

[0036] Furthermore, in the phase control strategy for improving the transient stability of virtual synchronous renewable energy units described in this invention, step S105 includes:

[0037] Real-time monitoring of common point voltage U PCC The amplitude when U PCC When the condition returns to normal, it is determined that the fault has been cleared.

[0038] Once the fault has been confirmed to be cleared, immediately cancel the phase that was forcibly locked during the previous fault.

[0039] The system switches from phase control strategy back to virtual synchronization control, that is, it restores the traditional virtual synchronous machine control strategy. The internal potential phase is regenerated by frequency integration, restoring the integral relationship between phase and frequency.

[0040] After switching back to the traditional control strategy, the frequency remains at the rated frequency;

[0041] The active power output of the system will gradually converge to the active power reference value to ensure stable operation of the system.

[0042] The beneficial effects of this invention are:

[0043] Because the frequency is not constrained by the oscillation equation during the fault, but the phase is directly locked, even if the power angle does not diverge due to the phase jump into the unstable operating region, and the control strategy can be smoothly switched after the fault is cleared, which is of great significance for improving the transient stability of the virtual synchronous machine during faults. Attached Figure Description

[0044] To more clearly illustrate the technical solution of the present invention, the drawings used in the embodiments will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on the drawings without creative effort.

[0045] Figure 1 This is a schematic diagram of the power angle curve of the existing VSG technology.

[0046] Figure 2 A block diagram of the phase control strategy provided in an embodiment of the present invention.

[0047] Figure 3 This is a schematic diagram of the fault detection process provided in an embodiment of the present invention.

[0048] Figure 4 This is a schematic diagram of the phase calculation process provided in an embodiment of the present invention.

[0049] Figure 5 This is a schematic diagram of the phase-locking process provided in an embodiment of the present invention.

[0050] Figure 6 A flowchart illustrating the steps of the phase control strategy provided in an embodiment of the present invention.

[0051] Figure 7 A schematic diagram comparing the active power of phase control and traditional control strategies in response to Type II instability.

[0052] Figure 8A diagram showing the frequency comparison between phase control and traditional control strategies for dealing with type II instability.

[0053] Figure 9 A schematic diagram comparing the terminal voltage for phase control and traditional control strategies in response to type II instability. Detailed Implementation

[0054] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with specific embodiments and corresponding drawings. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention. The technical solutions provided by various embodiments of this invention will be described in detail below with reference to the accompanying drawings.

[0055] To better understand the purpose of this invention, the invention will now be described in further detail.

[0056] This invention provides a phase control strategy for improving the transient stability of virtual synchronous renewable energy units, comprising:

[0057] S101: Fault detection steps: acquire system data, utilize fault detection on the acquired data, and measure the common point voltage U in real time. PCC Amplitude, monitoring whether the system malfunctions, if U PCC If the value is less than 0.9pu, the system is considered to have a fault, and the fault signal changes from low level to high level after a rising edge.

[0058] The specific steps for fault detection of S101 are as follows: acquire system data and use fault detection to measure the common point voltage U in real time. PCC The amplitude is used to monitor whether a system malfunction has occurred. If U PCC If the amplitude is less than 0.9 pu, the system is considered to have a fault. At this time, the fault signal changes from low level to high level after a rising edge.

[0059] S102: Phase-locking step. When the system detects a fault, the phase-locking circuit locks the phase of the internal potential and terminal voltage at the instant of the fault. The fault signal generated by the fault detection circuit is introduced, and the trigger is activated by the rising edge of the fault signal changing from 0 to 1, locking the phase θ of the internal potential at this moment. E and terminal voltage phase θ U Calculate and lock the difference δ0 between the two;

[0060] The specific steps of the S102 phase-locking procedure are as follows: When the system detects a fault, the phase-locking circuit locks the phase of the internal potential and the terminal voltage at the instant of the fault. A fault signal generated by the fault detection circuit is introduced, and the trigger is activated by the rising edge of the fault signal changing from 0 to 1, locking the phase θ of the internal potential at this moment. E and terminal voltage phase θ U And calculate and lock the difference δ0 between the two.

[0061] S103: Phase control and frequency locking steps, during system faults, utilize the phase calculation stage to calculate the terminal voltage phase θ in real time. U And lock the internal potential phase at θ U +δ0, and control the frequency separately, locking the frequency to the grid frequency ω. g ;

[0062] The detailed operation steps for S103 phase control and frequency locking are as follows:

[0063] To maintain the transient stability of the system during a failure, special control measures are required. First, the phase θ of the terminal voltage is calculated in real time using a phase calculation module. U This is typically accomplished by extracting the direct-axis and quadrature-axis components of the terminal voltage and applying a preset formula.

[0064] Next, we lock the phase of the internal potential to the phase θ of the terminal voltage. U Adding the previously calculated and locked phase difference δ0, i.e. θ E =θ U +δ0. The purpose of this is to ensure that the phase difference between the internal potential and the terminal voltage remains constant during a fault, thereby preventing the power angle from diverging.

[0065] Meanwhile, in order to maintain the system's frequency stability, we control the frequency separately and lock it to the grid frequency ω. g This helps the system quickly return to its rated frequency after a fault is cleared, avoiding drastic frequency fluctuations.

[0066] In summary, step S103 effectively maintains the transient stability of the system during a fault by calculating the terminal voltage phase in real time, locking the internal potential phase, and controlling the frequency.

[0067] S104: Fault clearing detection step. Continue to use fault detection to determine whether the fault has been cleared. If the fault has been cleared, prepare to switch back to the traditional control strategy; otherwise, continue to execute the phase control and frequency locking steps.

[0068] The detailed operating instructions for clearing and detecting S104 faults are as follows:

[0069] After a fault occurs and corresponding phase control and frequency locking measures are taken, the system needs to continuously monitor the fault status to determine when it can switch back to the traditional control strategy.

[0070] Continuous fault detection: Utilizing the previously mentioned fault detection steps, the common point voltage U is continuously measured in real time. PCC The amplitude. Monitoring U PCC Whether the amplitude recovers to above the set threshold (e.g., ≥0.9pu) is used as the basis for determining whether the fault has been cleared.

[0071] Fault clearing judgment: If the common point voltage U PCC If the amplitude of the fault signal recovers to above the set threshold and remains above it for a period of time (to ensure that the fault is indeed cleared and not just a momentary fluctuation), then the fault is considered to have been cleared. At this time, the fault signal will change from a high level to a low level, indicating that the fault state has been resolved.

[0072] Control strategy switching preparation: Once the fault is confirmed to be cleared, the system needs to prepare to switch back from the current phase control and frequency locking strategy to the traditional virtual synchronization control strategy. This includes canceling the previously forcibly locked phase and frequency, restoring the integral relationship between phase and frequency, and adjusting control parameters to adapt to normal operating conditions.

[0073] If the fault is not cleared (i.e., U) PCC If the amplitude is still below the set threshold, the system continues to perform phase control and frequency locking steps to maintain the transient stability of the system.

[0074] If the fault has been cleared, the system will smoothly switch back to the traditional virtual synchronous control strategy according to the predetermined procedure, ensuring that the system can stably recover to its pre-fault operating state.

[0075] Through the S104 fault clearing detection step, the system can promptly detect the fault clearing status and make corresponding control strategy adjustments based on the actual situation to ensure stable system operation and rapid recovery.

[0076] S105: Normal operation restoration procedure. After the fault is cleared, a virtual internal potential phase is generated based on the virtual synchronization control link, the forced locking phase is canceled, the system switches back to the traditional control strategy, normal operation is restored, the voltage rises, the fault signal changes from high level to low level after a falling edge, and the system returns to the operating state before the fault.

[0077] The detailed instructions for restoring S105 to normal operation are as follows:

[0078] The common point voltage U is continuously monitored through the fault detection process. PCCThe amplitude of the fault signal is checked to confirm that it has stabilized and recovered to above the set threshold (e.g., ≥0.9pu), and the fault signal has changed from high level to low level, indicating that the fault has indeed been cleared.

[0079] Once the fault is confirmed to be cleared, the internal potential phase that was previously forcibly locked to maintain transient stability is immediately removed. This means that the internal potential phase is no longer locked to the terminal voltage phase θ. U Instead of adding the position of the phase difference δ0, it allows it to be freely generated according to the virtual synchronization control link.

[0080] With the phase lock removed, the system gradually switches back to the traditional virtual synchronization control strategy. This includes restoring the integral relationship between phase and frequency, and adjusting control parameters according to the actual operating state of the system.

[0081] During the switchback to the traditional control strategy, the system needs to ensure that the frequency remains near the rated frequency ω0 to avoid system instability caused by frequency fluctuations. Simultaneously, the system's output active power will gradually converge to the active power reference value, ensuring power balance and stable operation of the system.

[0082] As the fault is cleared and the control strategy is switched, the common point voltage U PCC It will gradually return to normal levels. The overall operating status of the system will also gradually return to the stable state before the fault, including the stabilization of parameters such as voltage, current, and power.

[0083] After resuming normal operation, the system needs to continuously monitor parameter changes to ensure long-term stable operation. If any anomalies or potential problems are detected, the system should be adjusted promptly or necessary protective measures should be taken.

[0084] By implementing the S105 procedure to restore normal operation, the system can quickly and smoothly return to its previous operating state after the fault is cleared, ensuring the safe, stable and reliable operation of the power system.

[0085] Specifically, the phase control strategy for improving the transient stability of virtual synchronous renewable energy units according to the present invention includes step S101, which includes:

[0086] The common point voltage U is measured in real time using the fault detection process. PCC The amplitude;

[0087] The system is being monitored for faults, specifically based on the common point voltage U. PCC Is the amplitude less than 0.9 pu?

[0088] If U PCC If the amplitude is less than 0.9 pu, the system is considered to have malfunctioned;

[0089] If the fault signal changes from low level to high level after a rising edge, then a system fault has occurred.

[0090] Specifically, in the phase control strategy for improving the transient stability of virtual synchronous renewable energy units described in this invention, the detailed implementation process of step S101 (fault detection step) is as follows:

[0091] By utilizing the fault detection stage, the common point voltage U is obtained from the power system in real time. PCC The data.

[0092] Continuous monitoring of the acquired data is necessary to gain real-time insight into U. PCC The amplitude changes.

[0093] A threshold value, i.e., the common point voltage U, is preset to determine whether a system fault has occurred. PCC Is the amplitude less than 0.9pu?

[0094] This threshold is determined based on the stable operation experience and safety standards of the power system, and is used to distinguish between normal operating conditions and possible fault conditions.

[0095] During real-time monitoring, if U is detected PCC If the amplitude is less than 0.9 pu, the system is immediately determined to have a fault. This determination is based on a previously set threshold and is the core part of the fault detection process.

[0096] When the system detects a fault, the fault detection circuit generates a fault signal. The fault signal is initially low, but it rises to high on a rising edge when a fault occurs. The high-level state of the fault signal indicates that the system is currently in a fault state, requiring appropriate control measures to maintain the system's transient stability.

[0097] In summary, step S101 involves real-time measurement of the common point voltage U. PCC The amplitude of the fault signal is monitored, and it is checked whether it is less than a set threshold (0.9 pu) to determine whether a system fault has occurred. When a fault is detected, the fault signal changes from low level to high level, thereby triggering subsequent control strategies to deal with the fault situation. This is an important part of the phase control strategy for improving the transient stability of virtual synchronous renewable energy units in this invention.

[0098] Specifically, the phase control strategy for improving the transient stability of virtual synchronous renewable energy units according to the present invention includes step S102, which includes:

[0099] By measuring the common point voltage U in real time PCC The amplitude is used to monitor whether a fault has occurred in the current system. If U PCCIf the amplitude is less than 0.9pu, the system is considered to have a fault, and the fault signal changes from low level to high level after a rising edge;

[0100] When the fault signal changes from 0 to 1 on a rising edge, the phase-locked loop is activated to lock the internal potential (θ) at the moment of the fault. E ) and terminal voltage (θ) U The phase of )

[0101] Simultaneously with triggering phase locking, the phase difference δ0 between the internal potential and the terminal voltage is calculated. This is achieved by locking the θ at the instant of the fault. E and θ U This is achieved by the phase difference δ0 being the difference between the two.

[0102] During a fault, the phase of the internal potential is locked to the phase of the terminal voltage plus a phase difference δ0, i.e., θ. E =θ U +δ0.

[0103] Specifically, in the phase control strategy for improving the transient stability of virtual synchronous renewable energy units described in this invention, the detailed implementation process of step S102 (phase locking step) is as follows:

[0104] By measuring the common point voltage U in real time PCC The amplitude is continuously monitored to determine if a fault has occurred in the current system. When U PCC When the amplitude is less than 0.9 pu, the system is considered to have a fault. At this time, the fault detection circuit will generate a fault signal from low level to high level, that is, the fault signal changes from 0 to 1. The rising edge of the fault signal is used as a trigger signal to start the phase locking circuit.

[0105] When a fault signal is triggered, the phase-locked loop is activated immediately. The phase-locked loop is designed to quickly and accurately lock the internal potential (θ) at the moment a fault occurs. E ) and terminal voltage (θ) U The phase of ).

[0106] Simultaneously with triggering phase locking, the locked internal potential phase θ is utilized E and terminal voltage phase θ U Calculate the phase difference δ0 between the two.

[0107] The phase difference δ0 is calculated using a simple subtraction operation, i.e., δ0 = θ. E -θ U (Note that the calculation here is based on the phase value at the instant of locking). The phase difference δ0 represents the phase relationship between the potential and the terminal voltage at the instant of the fault, and is a parameter in the subsequent control strategy.

[0108] During a fault, to maintain the transient stability of the system, the phase of the internal potential needs to be locked at a specific value. Based on the previously calculated phase difference δ0, the phase of the internal potential is locked at the position where the phase of the terminal voltage is added to the phase difference δ0, i.e., θ. E =θ U +δ0. The purpose of this is to ensure that the phase difference between the internal potential and the terminal voltage remains constant during a fault, thereby preventing the divergence of the power angle and the instability of the system.

[0109] In summary, step S102, through a series of operations such as real-time monitoring of fault signals, activation of the phase-locking mechanism, calculation of phase difference δ0, and locking of the internal potential phase, achieves rapid locking and control of the internal potential and terminal voltage phase at the moment of fault, providing important support for subsequent fault handling and system recovery.

[0110] Specifically, the phase control strategy for improving the transient stability of virtual synchronous renewable energy units according to the present invention includes step S103, which includes:

[0111] Real-time measurement of common point voltage U PCC The amplitude, if U PCC If the amplitude is less than 0.9 pu, the system is considered to have malfunctioned;

[0112] The fault signal changes from low to high via a rising edge. A trigger is used to lock the phase of the internal potential and terminal voltage at the instant of the fault. The trigger is activated by the rising edge of the fault signal changing from 0 to 1, locking the phase θ of the internal potential at that moment. E and terminal voltage phase θ U The phase difference δ0 between the two is calculated.

[0113] The direct-axis and quadrature-axis components of the terminal voltage are extracted in real time, and the current terminal voltage phase θ is calculated using a preset formula. U The final terminal voltage phase is obtained after low-pass filtering.

[0114] Lock the internal potential phase at θ U If +δ0, then the phase is stable during the fault period;

[0115] Lock the frequency to the grid frequency ω g This is used to avoid frequency shift after fault clearance;

[0116] The fault detection is used to determine whether the fault has been cleared. If the fault has been cleared, the locked phase is released, the system switches back to the traditional virtual synchronous control strategy, the voltage rises, the fault signal goes low, and the system recovers.

[0117] Specifically, in the phase control strategy for improving the transient stability of virtual synchronous renewable energy units described in this invention, the detailed implementation process of step S103 (phase control and frequency locking step) is as follows:

[0118] Real-time measurement of common point voltage U PCC The amplitude is used as a basis for judging whether the system has malfunctioned.

[0119] If U PCC If the amplitude is less than 0.9 pu, a system fault is confirmed, and the fault signal changes from low level to high level.

[0120] A trigger is used, which is activated by the rising edge of the fault signal changing from 0 to 1, to lock the internal potential phase θ at the moment of the fault. E and terminal voltage phase θ U .

[0121] The phase difference δ0 between the two is calculated. This phase difference is a direct reflection of the phase relationship between the internal potential and the terminal voltage at the moment of the fault.

[0122] Real-time extraction of the direct-axis and quadrature-axis components of the terminal voltage is typically accomplished using a voltage sensor and related signal processing circuitry. The current terminal voltage phase θ is then calculated using a preset formula based on the direct-axis and quadrature-axis components. U To eliminate potential noise and interference, the calculated terminal voltage phase is low-pass filtered to obtain the final terminal voltage phase.

[0123] Lock the internal potential phase at θ U The +δ0 position ensures that the phase difference between the internal potential and the terminal voltage remains constant even during a fault, thus ensuring the transient stability of the system.

[0124] Lock the system frequency to the grid frequency ω. g This is to avoid a shift in the system frequency after a fault is cleared, thereby ensuring stable system operation.

[0125] The fault detection process continuously monitors the fault status to determine whether the fault has been cleared. If the fault is cleared (i.e., U... PCC If the amplitude recovers to above the set threshold and remains above it for a period of time, the previously locked phase is canceled, allowing the system to freely adjust the phase of the internal potential according to the virtual synchronization control strategy.

[0126] Simultaneously, the system switched back to the traditional virtual synchronous control strategy, the voltage gradually recovered to normal levels, and the fault signal changed from high level to low level. At this point, the system returned to its pre-fault operating state and continued to provide a stable and reliable power supply to the grid.

[0127] In summary, step S103 achieves effective control of the phase and frequency of the virtual synchronous new energy unit during a fault by performing a series of operations, including real-time monitoring of the fault status, locking the phase difference at the moment of the fault, real-time calculation of the terminal voltage phase, locking the internal potential phase and frequency, and detecting fault clearing and restoring system operation. This improves the transient stability of the unit.

[0128] Specifically, the phase control strategy for improving the transient stability of virtual synchronous renewable energy units according to the present invention includes step S104, which includes:

[0129] After a system failure occurs, the fault detection process will generate a fault signal;

[0130] To determine whether the fault has been cleared, the common point voltage U is measured in real time through the fault detection process. PCC The amplitude;

[0131] If the common point voltage U PCC If the amplitude recovers to above the set threshold, the fault is considered to have been cleared.

[0132] At this point, the fault signal changes from high level to low level after a falling edge, indicating that the fault has been eliminated.

[0133] The system triggers a control strategy switch. When the fault signal is detected to go low, the system confirms that the fault has been cleared. After confirming that the fault has been cleared, the system triggers the control strategy switch mechanism to switch back from the phase control strategy to the virtual synchronous traditional control strategy.

[0134] After switching back to the traditional control strategy, the system will regenerate the virtual internal potential phase based on the virtual synchronization control link, lock the frequency to the grid frequency, and the output active power will quickly converge to the active power reference value. The system will then return to the stable operating state before the fault, achieving transient stability.

[0135] Specifically, in the phase control strategy for improving the transient stability of virtual synchronous renewable energy units described in this invention, the detailed implementation process of step S104 (fault clearing detection and strategy switching step) is as follows:

[0136] After a system failure occurs, the fault detection circuit immediately generates and continuously sends a fault signal, which is typically high-level, indicating that the system is currently in a fault state. The common point voltage U is measured in real time through the fault detection circuit. PCC The amplitude is used as the main basis for judging whether the fault has been cleared.

[0137] Set a threshold (e.g., 0.9 pu) if the common point voltage U PCCIf the amplitude recovers to above the threshold and remains there for a period of time (to ensure it is not a momentary fluctuation), the fault is considered to have been cleared. When the fault is confirmed to have been cleared, the fault detection circuit changes the state of the fault signal from a high level to a low level after a falling edge, indicating that the fault has been eliminated.

[0138] The system continuously monitors the status of fault signals. Once a fault signal is detected to go low, it confirms that the fault has been cleared. At this point, the system triggers the control strategy switching mechanism, preparing to switch from the current phase control strategy back to the virtual synchronous traditional control strategy.

[0139] During the switching process, the system regenerates the virtual internal potential phase based on the virtual synchronization control loop. This phase is no longer controlled by the previous phase-locking loop, but is dynamically adjusted according to the actual operating state of the system and the control algorithm of the virtual synchronizer. Simultaneously, the system frequency remains locked to the grid frequency ω. g This is to ensure that the frequency does not shift during the switching process.

[0140] As the control strategy is switched, the active power output of the system will quickly converge to the active power reference value, which is an important sign that the system has returned to a stable operating state.

[0141] After the control strategy is switched, the system will continue to monitor the changes in parameters in order to restore the system to the stable operating state before the failure.

[0142] At this point, the system's voltage, current, power, and other parameters should return to normal levels and remain stable. Through this series of operations, the system successfully transitioned from a fault state to a stable state, improving the transient stability of the virtual synchronous renewable energy unit.

[0143] In summary, step S104 achieves a smooth switching of the system control strategy and rapid system recovery after the fault is cleared through a series of operations, including real-time monitoring of fault signals, determining whether the fault has been cleared, triggering control strategy switching, switching back to the traditional control strategy, and confirming that the system has recovered to stability.

[0144] Specifically, the phase control strategy for improving the transient stability of virtual synchronous renewable energy units according to the present invention includes step S105, which includes:

[0145] Real-time monitoring of common point voltage U PCC The amplitude when U PCC When the condition returns to normal, it is determined that the fault has been cleared.

[0146] Once the fault has been confirmed to be cleared, immediately cancel the phase that was forcibly locked during the previous fault.

[0147] The system switches from phase control strategy back to virtual synchronization control, that is, it restores the traditional virtual synchronous machine control strategy. The internal potential phase is regenerated by frequency integration, restoring the integral relationship between phase and frequency.

[0148] After switching back to the traditional control strategy, the frequency remains at the rated frequency;

[0149] The active power output of the system will gradually converge to the active power reference value to ensure stable operation of the system.

[0150] Specifically, in the phase control strategy for improving the transient stability of virtual synchronous new energy units described in this invention, the detailed implementation process of step S105 (restoring the traditional virtual synchronous control steps) is as follows:

[0151] Real-time monitoring of common point voltage U PCC The amplitude is used as a direct basis for judging whether the fault has been cleared.

[0152] When U PCC Once the amplitude stabilizes and returns to the normal range (e.g., greater than or equal to 0.9 pu and remains so for a period of time), the system confirms that the fault has been cleared.

[0153] Once the fault has been confirmed to be cleared, the system immediately cancels the internal potential phase that was forcibly locked during the fault to maintain transient stability. This means that the internal potential phase is no longer constrained by the control strategy during the fault and will instead resume its normal dynamic adjustment mechanism.

[0154] The system smoothly switches from the current phase control strategy back to the traditional virtual synchronization control loop. Under the traditional virtual synchronization control strategy, the internal potential phase is regenerated by frequency integration, that is, the integral relationship between phase and frequency is restored. This is an important part of the virtual synchronous machine simulating the characteristics of a traditional synchronous generator.

[0155] After switching back to the traditional control strategy, the system frequency remains at the grid frequency ω. g Because the system had already ensured frequency stability through a frequency locking mechanism during the fault, this stability was maintained after switching back to the traditional control strategy, preventing sudden frequency changes from impacting the system.

[0156] As the control strategy switches and the system state recovers, the system's output active power will gradually converge to the active power reference value. One of the important indicators that the system has returned to a stable operating state is that the system is able to operate stably according to the predetermined power output requirements.

[0157] After completing the above steps, the system enters a stable operation phase. At this time, the system's voltage, current, power, and other parameters should remain within the normal range, and the system should be able to respond and adjust quickly to changes in external load or minor disturbances.

[0158] In summary, step S105, through a series of operations such as real-time monitoring of fault clearance, cancellation of phase locking, switching back to the traditional control strategy, maintaining frequency stability, and ensuring active power convergence, achieves a smooth transition from the phase control strategy to the traditional virtual synchronization control strategy after fault clearance, ensuring stable system operation and rapid recovery.

[0159] This invention proposes a phase control strategy to improve the transient stability of virtual synchronous renewable energy units. According to... Figure 2 The diagram shows the connection of the inputs and outputs of the four related stages, resulting in a complete phase control strategy block diagram. During normal operation, the system employs a virtual synchronous control stage (solid line box), controlling the frequency via an active-frequency loop (1), and obtaining the internal potential phase (2) through frequency integration. When the common point voltage U... PCC When the value is less than 0.9 pu, the system is considered to have malfunctioned. To avoid instability caused by excessive phase jumps, the system switches to a phase control strategy (dashed box).

[0160]

[0161] Where J is the virtual moment of inertia, ω is the frequency, ω0 is the rated frequency, and P ref It is the active power reference value, P e It is the output active power, D is the damping coefficient, and δ is the power angle.

[0162] After the fault disappears, the forced phase lockout is released. At this point, the voltage recovers, the fault signal transitions from 1 to 0, and the system switches back to the traditional control strategy. This phase transition is caused by the topology change. When the topology recovers, the phase immediately returns to its pre-fault value, and the system returns to its pre-fault operating state. After switching back to the traditional control strategy, the frequency is the control frequency during the fault, i.e., the grid frequency. The output active power will not deviate significantly and will quickly converge to the active power reference value. The following describes the content of each module and its implementation method.

[0163] In the fault detection phase, the common point voltage U is measured in real time. PCC Amplitude, used to monitor whether a fault has occurred in the current system. If U PCC If the value is less than 0.9 pu, a fault is considered to have occurred, and the fault signal changes from a low level to a high level after a rising edge.

[0164] In the phase calculation stage, the direct-axis and quadrature-axis components of the terminal voltage are extracted in real time, and the current terminal voltage phase is calculated by (3). In order to eliminate the phase change caused by electromagnetic transients, a low-pass filter is used to obtain the final terminal voltage phase θ. U .

[0165]

[0166] Where ui is the quadrature-axis component of the terminal voltage and ur is the direct-axis component of the terminal voltage.

[0167] The phase-locked loop uses two triggers to lock the phase of the potential and terminal voltage at the instant of a fault. A fault signal generated by the fault detection loop is introduced; the triggers are activated by the rising edge of the fault signal changing from 0 to 1, locking the phase θ at that moment. E and θ U Thus, the difference between the two is locked, δ0(3-4).

[0168] δ0=θ E -θ U (4)

[0169] In the frequency control stage, if no special frequency control is implemented during a fault, the difference in active power will cause a significant frequency shift. After the fault is cleared, switching back to the traditional control strategy will result in a frequency shift that affects the stability of active power. To achieve a smooth transition between control modes, separate frequency control is required. During the fault, a control frequency equal to the grid frequency is maintained to prevent excessive active power feedback caused by the frequency shift after fault clearance. Since there is no integral relationship between frequency and phase during a fault, frequency control and the aforementioned phase control are not contradictory.

[0170] This invention proposes a phase control strategy to improve the transient stability of virtual synchronous renewable energy units. The specific flowchart is as follows: Figure 6 As shown.

[0171] Step 1: Utilize the fault detection step to detect if a fault has occurred and generate a fault signal. If a fault occurs, proceed to Step 2; otherwise, proceed to Step 6.

[0172] Step 2: Use a phase-locked loop to lock the phase of the internal potential and terminal voltage at the moment of the fault, and calculate the phase difference δ0.

[0173] Step 3: Calculate the terminal voltage phase θ in real time using the phase calculation step. U Locking the internal potential phase at θ U +δ0

[0174] Step 4: Lock the frequency to the grid frequency ω g ;

[0175] Step 5: Using the fault detection step, determine whether the fault has been cleared. If the fault has been cleared, proceed to Step 6; otherwise, proceed to Step 3.

[0176] Step 6: Generate a virtual internal potential phase based on the virtual synchronization control loop, and restore normal operation.

[0177] Simulated operating conditions;

[0178]

[0179] Table 1 Simulation Parameters

[0180] The fault is set to occur in 0.1s and clear in 4s. The fault transition resistance is 0.00625 + j0.0065p.u., and the system-side reactance is 0.03pu. Substituting the data into formula (2-3), we can calculate that the external equivalent voltage phase jump is -35.2°. The phase jump before and after the fault is large, and the power angle after the jump is in the unstable operating region.

[0181] By referring to Figure 7 , Figure 8 as well as Figure 9 Under traditional control strategies, a three-phase short circuit in this operating condition causes a drop in terminal voltage and oscillations, resulting in oscillations and negative values ​​in active power, an increase in frequency, and system instability. This instability is a type II instability, where the phase jump is too large after a system fault, entering an unstable operating region. The difference in active power leads to an increase in frequency, which is always greater than the rated frequency. This is the fundamental reason for the power angle divergence and continuous oscillation of active power.

[0182] This patent switches to a phase control strategy after a 0.1s fault, and the internal potential... Locked at θ u +δ0 prevents power angle divergence. During the fault, the frequency stabilizes at 1 p.u., at which point there is no integral relationship between phase and frequency. When the fault is cleared at 4 seconds, the system switches back to the traditional control strategy, at which point the frequency is the rated frequency, restoring the integral relationship between phase and frequency. Therefore, a smooth frequency switching can be achieved. Oscillations during active power faults are effectively suppressed, and the system can quickly transition to a stable value after the fault occurs and is cleared. The terminal voltage remains at 0.67 p.u. during the fault, achieving transient stability.

[0183] The technical solution proposed in this invention solves the problem that during a fault, the potential phase is no longer generated by frequency integration, but instead tracks the terminal voltage phase, maintaining the phase difference between the two at the instant of the fault, thus preventing the divergence of the power angle. Simultaneously, it achieves a smooth switchback to the virtual synchronous traditional control strategy after the fault, and locks the control frequency to the grid frequency ω during the fault. g To address the instability caused by excessive phase jumps during a fault:

[0184] Fault detection steps: Real-time measurement of the common point voltage U PCC The amplitude when U PCC When the value is less than 0.9 pu, the system is considered to have a fault, and the fault signal changes from low level to high level.

[0185] Phase-locking procedure: When the system detects a fault, the phase-locking circuit locks the internal potential (θ) at the instant of the fault. E ) and terminal voltage (θ) U The phase of θ is calculated and locked. The phase difference δ0 between the two is calculated and locked, i.e., θ E =θ U +δ0.

[0186] Phase control and frequency locking steps: During system faults, the terminal voltage phase θ is calculated in real time. U And lock the internal potential phase at θ U +δ0. Simultaneously, the frequency is controlled independently, locking it to the grid frequency ω. g .

[0187] Fault clearing detection steps: Continue to use fault detection to determine whether the fault has been cleared. If the fault has been cleared, prepare to switch back to the traditional control strategy; otherwise, continue with the phase control and frequency locking steps.

[0188] Normal operation restoration procedure: After the fault is cleared, a virtual internal potential phase is generated based on the virtual synchronization control loop, the forced locking phase is canceled, and the system switches back to the traditional control strategy, restoring normal operation. At this time, the voltage rises, and the fault signal changes from high level to low level.

[0189] Preventing power angle divergence: By locking the phase difference between the internal potential and the terminal voltage at the moment of the fault, the power angle is kept from diverging during the fault, thereby ensuring transient stability.

[0190] Smooth switching: After the fault is cleared, the system can smoothly switch from the phase control strategy back to the virtual synchronous traditional control strategy. Because the frequency is locked to the grid frequency during the fault, the frequency will not deviate from the rated value after the switch, avoiding drastic fluctuations in active power.

[0191] Addressing excessive phase jumps during faults: By locking the phase difference at the moment of a fault, this invention can effectively address the instability caused by excessive phase jumps during a fault, thereby improving the transient stability of virtual synchronous new energy units.

[0192] In summary, the technical solution of this invention successfully solves the problem of controlling the potential phase during a fault by using precise phase locking, frequency control, and fault detection and clearing mechanisms, and achieves smooth switching after a fault, thereby improving the transient stability of the virtual synchronous new energy unit.

Claims

1. A phase control strategy for improving the transient stability of virtual synchronous renewable energy units, characterized in that, include: S101: Fault detection steps: acquire system data, utilize fault detection on the acquired data, and measure the common point voltage U in real time. PCC Amplitude, monitoring whether the system malfunctions, if U PCC If the value is less than 0.9pu, the system is considered to have a fault, and the fault signal changes from low level to high level after a rising edge. S102: Phase-locking step. When the system detects a fault, the phase-locking circuit locks the phase of the internal potential and terminal voltage at the instant of the fault. The fault signal generated by the fault detection circuit is introduced, and the trigger is activated by the rising edge of the fault signal changing from 0 to 1, locking the phase θ of the internal potential at this moment. E and terminal voltage phase θ U Calculate and lock the difference δ0 between the two; S103: Phase control and frequency locking steps, during system faults, utilize the phase calculation stage to calculate the terminal voltage phase θ in real time. U And lock the internal potential phase at θ U +δ0, and control the frequency separately, locking the frequency to the grid frequency ω. g ; S104: Fault clearing detection step. Continue to use fault detection to determine whether the fault has been cleared. If the fault has been cleared, prepare to switch back to the traditional control strategy; otherwise, continue to execute the phase control and frequency locking steps. S105: Normal operation restoration procedure. After the fault is cleared, a virtual internal potential phase is generated based on the virtual synchronization control link, the forced locking phase is canceled, the system switches back to the traditional control strategy, normal operation is restored, the voltage rises, the fault signal changes from high level to low level after a falling edge, and the system returns to the operating state before the fault.

2. The phase control strategy for improving the transient stability of virtual synchronous new energy units as described in claim 1, characterized in that, Step S101 includes: The common point voltage U is measured in real time using the fault detection process. PCC The amplitude; The system is being monitored for faults, specifically based on the common point voltage U. PCC Is the amplitude less than 0.9 pu? If U PCC If the amplitude is less than 0.9 pu, the system is considered to have malfunctioned; If the fault signal changes from low level to high level after a rising edge, then a system fault has occurred.

3. The phase control strategy for improving the transient stability of virtual synchronous new energy units as described in claim 1, characterized in that, Step S102 includes: By measuring the common point voltage U in real time PCC The amplitude is used to monitor whether a fault has occurred in the current system. If U PCC If the amplitude is less than 0.9pu, the system is considered to have a fault, and the fault signal changes from low level to high level after a rising edge; When the fault signal changes from 0 to 1 on a rising edge, the phase-locked loop is activated to lock the internal potential (θ) at the moment of the fault. E ) and terminal voltage (θ) U The phase of ) Simultaneously with triggering phase locking, the phase difference δ between the internal potential and the terminal voltage is calculated. 0； This is achieved by locking the θ at the moment of failure. E and θ U This is achieved by the phase difference δ0 being the difference between the two. During a fault, the phase of the internal potential is locked to the phase of the terminal voltage plus a phase difference δ0, i.e., θ. E =θ U +δ0.

4. The phase control strategy for improving the transient stability of virtual synchronous new energy units as described in claim 1, characterized in that, Step S103 includes: Real-time measurement of common point voltage U PCC The amplitude, if U PCC If the amplitude is less than 0.9 pu, the system is considered to have malfunctioned; The fault signal changes from low to high via a rising edge. A trigger is used to lock the phase of the internal potential and terminal voltage at the instant of the fault. The trigger is activated by the rising edge of the fault signal changing from 0 to 1, locking the phase θ of the internal potential at that moment. E and terminal voltage phase θ U The phase difference δ0 between the two is calculated. The direct-axis and quadrature-axis components of the terminal voltage are extracted in real time, and the current terminal voltage phase θ is calculated using a preset formula. U The final terminal voltage phase is obtained after low-pass filtering. Lock the internal potential phase at θ U If +δ0, then the phase is stable during the fault period; Lock the frequency to the grid frequency ω g This is used to avoid frequency shift after fault clearance; The fault detection is used to determine whether the fault has been cleared. If the fault has been cleared, the locked phase is released, the system switches back to the traditional virtual synchronous control strategy, the voltage rises, the fault signal goes low, and the system recovers.

5. The phase control strategy for improving the transient stability of virtual synchronous new energy units as described in claim 1, characterized in that, Step S104 includes: After a system failure occurs, the fault detection process will generate a fault signal; To determine whether the fault has been cleared, the common point voltage U is measured in real time through the fault detection process. PCC The amplitude; If the common point voltage U PCC If the amplitude recovers to above the set threshold, the fault is considered to have been cleared. At this point, the fault signal changes from high level to low level after a falling edge, indicating that the fault has been eliminated. The system triggers a control strategy switch. When the fault signal is detected to go low, the system confirms that the fault has been cleared. After confirming that the fault has been cleared, the system triggers the control strategy switch mechanism to switch back from the phase control strategy to the virtual synchronous traditional control strategy. After switching back to the traditional control strategy, the system will regenerate the virtual internal potential phase based on the virtual synchronization control link, lock the frequency to the grid frequency, and the output active power will quickly converge to the active power reference value. The system will then return to the stable operating state before the fault, achieving transient stability.

6. The phase control strategy for improving the transient stability of virtual synchronous new energy units as described in claim 1, characterized in that, Step S105 includes: Real-time monitoring of common point voltage U PCC The amplitude when U PCC When the condition returns to normal, it is determined that the fault has been cleared. Once the fault has been confirmed to be cleared, immediately cancel the phase that was forcibly locked during the previous fault period; The system switches from phase control strategy back to virtual synchronization control, that is, it restores the traditional virtual synchronous machine control strategy. The internal potential phase is regenerated by frequency integration, restoring the integral relationship between phase and frequency. After switching back to the traditional control strategy, the frequency remains at the rated frequency; The active power output of the system will gradually converge to the active power reference value to ensure stable operation of the system.

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