Phase control strategy for improving transient stability of virtual synchronous new energy unit

Abstract

The invention relates to the technical field of data processing, provides a phase control strategy for improving transient stability of a virtual synchronous new energy unit, and aims to solve the problem of phase jump at the moment of a fault through a series of steps of fault detection, phase locking, phase control and frequency locking, fault clearing detection, normal operation recovery and the like. The potential phase tracks the terminal voltage phase in the fault period, the phase difference is kept constant, and power angle divergence is effectively prevented. Meanwhile, the frequency is locked at the power grid frequency, and it is ensured that the system can smoothly switch back to a traditional control strategy after the fault is cleared. According to the strategy, the problem of system instability caused by overlarge phase jump at the moment of fault is effectively solved, the transient stability of the virtual synchronous new energy unit is remarkably improved, and a powerful guarantee is provided for safe and stable operation of a power system.

Description

Technical Field

[0001] The present invention relates to the field of data processing technology, and in particular to a phase control strategy for improving the transient stability of a virtual synchronous new energy unit. Background Art

[0002] In recent years, with the changes in the global energy structure, the proportion of renewable energy power generation has increased year by year, while the proportion of traditional synchronous generators has continued to decline. Due to the randomness, volatility, and intermittency of renewable energy, the inertia and damping of the system continue to decrease, which makes the system in the transient process after large disturbances such as load shedding. The overcurrent caused by the voltage drop of the power grid will damage the power electronic devices, the system has a larger frequency change rate and frequency change range, and the transient stability becomes worse, which seriously threatens the safety of the power system.

[0003] In order to improve the transient stability of renewable energy after it is connected to the power grid, domestic and foreign scholars simulated the characteristics of synchronous generators and proposed virtual synchronous machine technology, which enables the inverter to have similar damping, inertia characteristics and voltage and frequency output external characteristics as synchronous generators, thereby improving the transient characteristics of the system. For renewable energy under virtual synchronous control, power, inertia, frequency, and phase are all artificially constructed and can be quickly controlled, which provides a variety of possible ways to enhance the transient stability of virtual synchronous renewable energy faults. Some studies have been based on the power angle characteristics of virtual synchronous machines ( Figure 1 ) was analyzed and a transient control strategy for a virtual synchronous machine with adaptive adjustment of active power deviation was proposed. An adaptive coefficient was introduced to quickly adjust the reference value of active power during the fault, which improved the transient characteristics, but did not consider the phase jump at the moment of the fault. In fact, at the moment of the fault, due to the access of the grounding loop, the topology of the circuit suddenly changes, and the phase of the external equivalent voltage jumps. If the initial working point of the power angle jumps to the unstable operation area. Under the traditional control strategy of the virtual synchronous machine, the active power reference value in the unstable operation area is always greater than the output active power. The active difference causes the frequency to increase and form positive feedback, which eventually leads to instability. Summary of the invention

[0004] In view of the shortcomings of the existing technology, the present invention provides a phase control strategy for improving the transient stability of virtual synchronous new energy units. For the phase jump at the moment of fault, this patent designs a method to lock the internal potential after the fault. and terminal voltage The phase control strategy of the phase difference between the two. The potential phase during the fault period is no longer generated by frequency integration, but tracks the terminal voltage phase during the fault period, and the phase difference between the two is kept at the value at the moment of the fault to prevent the divergence of the power angle. After the fault, it switches back to the virtual synchronization traditional control strategy. In order to achieve smooth switching, the control frequency is locked at the grid frequency during the fault period. The proposed strategy can cope with the instability caused by excessive phase jump at the moment of the fault.

[0005] In order to solve the above technical problems, the specific technical solutions of the present invention are as follows:

[0006] The present invention provides a phase control strategy for improving the transient stability of a virtual synchronous new energy unit, including:

[0007] S101: Fault detection step, obtaining system data, using fault detection on the obtained data, and measuring the common point voltage U in real time PCC amplitude, monitor whether the system fails. If U PCC <0.9pu, the system is considered to have a fault, and the fault signal changes from a low level to a high level after a rising edge;

[0008] S102: Phase locking step. When the system detects a fault, the phase locking link is used to lock the phase of the internal potential and the terminal voltage at the moment of the fault. The fault signal generated by the fault detection link is introduced. The trigger is triggered by the rising edge of the fault signal 0 to 1, and the internal potential phase θ at this moment is locked. E and terminal voltage phase θ U , calculate and lock the difference δ0 between the two;

[0009] S103: Phase control and frequency locking step. During a system fault, the terminal voltage phase θ is calculated in real time using the phase calculation link. U , and lock the internal potential phase at θ U +δ0, and control the frequency separately to lock the frequency at the grid frequency ω g ;

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

[0011] S105: Step of resuming normal operation. When the fault is cleared, a virtual internal potential phase is generated according to the virtual synchronous control link, the forced locked phase is canceled, and the system switches back to the traditional control strategy to resume normal operation. The voltage rises, and the fault signal changes from a high level to a low level via 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 new energy units described in the present invention, step S101 includes:

[0013] Using the fault detection link, the common point voltage U is measured in real time PCC The amplitude of

[0014] Monitor whether the current system has a fault. The specific judgment basis is the common point voltage UPCC Is the amplitude less than 0.9pu?

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

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

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

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

[0019] When the fault signal changes from 0 to 1 on the rising edge, the phase locking link is enabled to lock the internal potential (θ E ) and terminal voltage (θ U )’s phase;

[0020] At the same time as the phase lock is triggered, the phase difference δ0 between the internal potential and the terminal voltage is calculated. This is achieved by locking the θ E and θ U To achieve this, the phase difference δ0 is the difference between the two;

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

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

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

[0024] The fault signal changes from low level to high level through a rising edge. The trigger is used to lock the phase of the internal potential and terminal voltage at the moment of the fault. The trigger is triggered by the rising edge of the fault signal from 0 to 1, and the internal potential phase θ is locked at this moment. E and terminal voltage phase θ U , calculate the phase difference δ0 between the two;

[0025] Extract the direct-axis and quadrature-axis components of the terminal voltage in real time, and calculate the current terminal voltage phase θ by a preset formula U , and the final terminal voltage phase is obtained through low-pass filtering;

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

[0027] Lock the frequency to the grid frequency ω g , used to avoid frequency deviation after fault removal;

[0028] Fault detection is used to determine whether the fault has been cleared. If the fault has been cleared, the locked phase is canceled and the control strategy is switched back to the traditional virtual synchronous control strategy. The voltage rises, the fault signal becomes a low level, and the system recovers.

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

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

[0031] Determine whether the fault is cleared and measure the common point voltage U in real time through the fault detection link PCC The amplitude of

[0032] If the common point voltage U PCC When the amplitude of is restored to above the set threshold, the fault is considered to have been cleared;

[0033] At this time, the fault signal changes from a high level to a low level through a falling edge, and the fault has been eliminated;

[0034] Trigger control strategy switching. When the fault signal is detected to be low level, the system confirms that the fault has been cleared. After confirming that the fault has been cleared, the system triggers the control strategy switching mechanism and switches from the phase control strategy back 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 synchronous control link, the frequency will be locked at the grid frequency, the output active power will quickly converge to the active power reference value, and the system will return to the stable operating state before the fault, achieving transient stability.

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

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

[0038] After confirming that the fault has been cleared, the phases that were forcefully locked during the previous fault are immediately cancelled.

[0039] The system switches from the phase control strategy back to the virtual synchronous control link, that is, the traditional virtual synchronous machine control strategy is restored, the internal potential phase is regenerated by the frequency integration, and the integral relationship between the phase and frequency is restored;

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

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

[0042] Beneficial effects of the present invention:

[0043] Because the frequency is not constrained by the swing equation during the fault, but the phase is directly locked. Even if the unstable operation area is entered due to the phase jump, the power angle will not diverge, and the control strategy can be smoothly switched after the fault is cleared, which is of great significance to improving the transient stability of the virtual synchronous machine fault. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] In order to more clearly illustrate the technical solution of the present invention, the following is a brief introduction to the drawings required for use in the embodiments. Obviously, for ordinary technicians in this field, other drawings can be obtained based on the drawings without paying any creative labor.

[0045] Figure 1 Schematic diagram of VSG power angle curve in the prior art.

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

[0047] Figure 3 A schematic diagram of a fault detection link provided in an embodiment of the present invention.

[0048] Figure 4 A schematic diagram of a phase calculation process according to an embodiment of the present invention.

[0049] Figure 5 A schematic diagram of a phase locking link provided in an embodiment of the present invention.

[0050] Figure 6 A flow chart of the steps of the phase control strategy provided by an embodiment of the present invention.

[0051] Figure 7 Schematic diagram of active power comparison between phase and traditional control strategies in dealing with the second type of instability.

[0052] Figure 8Schematic diagram of phase and frequency comparison of traditional control strategies in dealing with the second type of instability.

[0053] Fig. 9 Schematic diagram of the comparison of terminal voltage of phase and traditional control strategies in dealing with the second type of instability. DETAILED DESCRIPTION

[0054] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be clearly and completely described in conjunction with the specific embodiments of the present invention and the corresponding drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention. The technical solutions provided by the embodiments of the present invention are described in detail below in conjunction with the drawings.

[0055] In order to better understand the purpose of the present invention, the present invention is described in further detail below.

[0056] The present invention provides a phase control strategy for improving the transient stability of a virtual synchronous new energy unit, including:

[0057] S101: Fault detection step, obtaining system data, using fault detection on the obtained data, and measuring the common point voltage U in real time PCC amplitude, monitor whether the system fails. If U PCC <0.9pu, the system is considered to have a fault, and the fault signal changes from a low level to a high level after a rising edge;

[0058] The specific contents of the S101 fault detection step are: obtaining system data and using fault detection to measure the common point voltage U in real time PCC to monitor whether the system has failed. PCC If the amplitude is less than 0.9pu, the system is considered to have a fault, and the fault signal changes from a low level to a high level through a rising edge.

[0059] S102: Phase locking step. When the system detects a fault, the phase locking link is used to lock the phase of the internal potential and the terminal voltage at the moment of the fault. The fault signal generated by the fault detection link is introduced. The trigger is triggered by the rising edge of the fault signal 0 to 1, and the internal potential phase θ at this moment is locked. E and terminal voltage phase θ U , calculate and lock the difference δ0 between the two;

[0060] The specific content of the phase locking step S102 is: when the system detects a fault, the phase locking link is used to lock the phase of the internal potential and the terminal voltage at the moment of the fault. The fault signal generated by the fault detection link is introduced, and the trigger is triggered by the rising edge of the fault signal 0 to 1, and the internal potential phase θ at this moment is locked. E and terminal voltage phase θ U , and calculate and lock the difference δ0 between the two.

[0061] S103: Phase control and frequency locking step. During a system fault, the terminal voltage phase θ is calculated in real time using the phase calculation link. U , and lock the internal potential phase at θ U +δ0, and control the frequency separately to lock the frequency at the grid frequency ω g ;

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

[0063] In order to maintain the transient stability of the system during a fault, we need to take special control measures. First, use the phase calculation link to calculate the phase θ of the terminal voltage in real time. U , which is usually done by extracting the direct and quadrature components of the terminal voltage and applying a preset formula.

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

[0065] At the same time, in order to keep the system frequency stable, we control the frequency separately and lock it at the grid frequency ω g This helps the system to quickly recover to the rated frequency after the fault is cleared and avoids drastic frequency fluctuations.

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

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

[0068] The detailed operation instructions for the S104 fault clearing detection steps 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 to switch back to the traditional control strategy.

[0070] Continuous fault detection: Using the fault detection link mentioned above, continue to measure the common point voltage U in real time PCC Monitor U PCC Whether the amplitude of the fault is restored to above the set threshold (for example, ≥0.9pu) is used as the basis for judging whether the fault is cleared.

[0071] Fault clearing judgment: If the common point voltage U PCC If the amplitude of the fault signal returns to above the set threshold and lasts for a period of time (to ensure that the fault is indeed cleared, rather than an instantaneous fluctuation), the fault is considered to have been cleared. At this time, the fault signal will change from the previous high level to a low level, indicating that the fault state has been resolved.

[0072] Preparation for control strategy switching: When it is confirmed that the fault has been cleared, the system needs to prepare to switch from the current phase control and frequency locking strategy back to the traditional virtual synchronization control strategy, including canceling the previously forced locked phase and frequency, restoring the integral relationship between phase and frequency, and adjusting the control parameters to adapt to normal operating conditions.

[0073] If the fault is not cleared (i.e. U PCC If the amplitude of the transient voltage is still lower than 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 to ensure that the system can stably return to the operating state before the fault.

[0075] Through the fault clearing detection step S104, the system can detect the clearing of the fault in a timely manner and make corresponding control strategy adjustments according to the actual situation to ensure stable operation and rapid recovery of the system.

[0076] S105: Step of resuming normal operation. When the fault is cleared, a virtual internal potential phase is generated according to the virtual synchronous control link, the forced locked phase is canceled, and the system switches back to the traditional control strategy to resume normal operation. The voltage rises, and the fault signal changes from a high level to a low level via a falling edge, and the system returns to the operating state before the fault.

[0077] The detailed instructions for the steps to restore normal operation of S105 are as follows:

[0078] Continuously monitor the common point voltage U through the fault detection link PCCThe amplitude of the fault signal is checked to confirm that it has been stably restored to above the set threshold (for example, ≥0.9pu), and the fault signal has changed from high level to low level, indicating that the fault has indeed been cleared.

[0079] After confirming that the fault has been cleared, the internal potential phase that was previously locked forcibly to maintain transient stability is immediately canceled. This means that the internal potential phase is no longer locked at the terminal voltage phase θ U Instead of adding the position of the phase difference δ0, it is allowed to be freely generated according to the virtual synchronous control link.

[0080] As the phase lock is canceled, the system begins to gradually switch back to the traditional virtual synchronous control strategy, which includes restoring the integral relationship between phase and frequency and adjusting the control parameters according to the actual operating status of the system.

[0081] In the process of switching back 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. At the same time, the active power output of the system will gradually converge to the active power reference value to ensure the 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 The system's overall operating status will also gradually return to the stable state before the fault, including the stability of parameters such as voltage, current, and power.

[0083] After resuming normal operation, the system needs to continuously monitor the changes in parameters to ensure the long-term stable operation of the system. If any abnormality or potential problems are found, the system should be adjusted in time or necessary protective measures should be taken.

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

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

[0086] Using the fault detection link, the common point voltage U is measured in real time PCC The amplitude of

[0087] Monitor whether the current system has a fault. The specific judgment basis is the common point voltage U PCC Is the amplitude less than 0.9pu?

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

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

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

[0091] Using the fault detection link, the common point voltage U is obtained from the power system in real time PCC data.

[0092] Continuously monitor the acquired data to obtain real-time information about the U PCC The amplitude change of .

[0093] A threshold value for judging whether the system fails is set in advance, that is, the common point voltage U 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 PCC If the amplitude is less than 0.9pu, the system is immediately judged to be faulty. The judgment is based on the previously set threshold and is the core part of the fault detection process.

[0096] When the system determines that a fault has occurred, the fault detection link will generate a fault signal. The fault signal is initially low, but when a fault occurs, it will change to a high level after a rising edge. The high level state of the fault signal indicates that the system is currently in a fault state, and corresponding control measures need to be taken to maintain the transient stability of the system.

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

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

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

[0100] When the fault signal changes from 0 to 1 on the rising edge, the phase locking link is enabled to lock the internal potential (θ E ) and terminal voltage (θ U )’s phase;

[0101] At the same time as the phase lock is triggered, the phase difference δ0 between the internal potential and the terminal voltage is calculated. This is achieved by locking the θ E and θ U To achieve this, the phase difference δ0 is the difference between the two;

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

[0103] Specifically, in the phase control strategy for improving the transient stability of the virtual synchronous new energy unit described in the present 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 of U continuously monitors whether the current system has any faults. PCC When the amplitude is less than 0.9pu, the system is considered to have a fault. At this time, the fault detection link 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 link.

[0105] When the fault signal is triggered, the phase locking link is immediately enabled. The phase locking link is designed to quickly and accurately lock the internal potential (θ E ) and terminal voltage (θ U ) phase.

[0106] While triggering the phase lock, the locked internal potential phase θ E and terminal voltage phase θ U , calculate the phase difference δ0 between the two.

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

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

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

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

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

[0112] The fault signal changes from low level to high level through a rising edge. The trigger is used to lock the phase of the internal potential and terminal voltage at the moment of the fault. The trigger is triggered by the rising edge of the fault signal from 0 to 1, and the internal potential phase θ is locked at this moment. E and terminal voltage phase θ U , calculate the phase difference δ0 between the two;

[0113] Extract the direct-axis and quadrature-axis components of the terminal voltage in real time, and calculate the current terminal voltage phase θ by a preset formula U , and the final terminal voltage phase is obtained through low-pass filtering;

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

[0115] Lock the frequency to the grid frequency ω g , used to avoid frequency deviation after fault removal;

[0116] Fault detection is used to determine whether the fault has been cleared. If the fault has been cleared, the locked phase is canceled and the control strategy is switched back to the traditional virtual synchronous control strategy. The voltage rises, the fault signal becomes a low level, and the system recovers.

[0117] Specifically, in the phase control strategy for improving the transient stability of the virtual synchronous new energy unit described in the present 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 the basis for judging whether the system fails.

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

[0120] Use a trigger that is triggered 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, which is a direct reflection of the phase relationship between the potential and the terminal voltage at the moment of the fault.

[0122] The direct-axis and quadrature-axis components of the terminal voltage are extracted in real time, which is usually done through a voltage sensor and related signal processing circuits. The current terminal voltage phase θ is calculated using the direct-axis and quadrature-axis components using a preset formula. U In order to eliminate possible 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 +δ0, so that even during a fault, the phase difference between the internal potential and the terminal voltage remains unchanged, thus ensuring the transient stability of the system.

[0124] Lock the system frequency to the grid frequency ω g ,This is to avoid the system frequency deviation after the fault is removed, thereby ensuring the stable operation of the system.

[0125] Use the fault detection link to continuously monitor the fault status and determine whether the fault has been cleared. PCC If the amplitude of the internal potential is restored to above the set threshold and lasts 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 synchronous control strategy.

[0126] At the same time, the system switches back to the traditional virtual synchronous control strategy, the voltage gradually rises to normal levels, and the fault signal changes from high level to low level. At this time, the system returns to the operating state before the fault and continues to provide stable and reliable power supply to the power grid.

[0127] In summary, step S103 realizes effective control of the phase and frequency of the virtual synchronous new energy unit during the fault period through a series of operations such as 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 clearance and restoring system operation, thereby improving the transient stability of the unit.

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

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

[0130] Determine whether the fault is cleared and measure the common point voltage U in real time through the fault detection link PCC The amplitude of

[0131] If the common point voltage U PCC When the amplitude of is restored to above the set threshold, the fault is considered to have been cleared;

[0132] At this time, the fault signal changes from a high level to a low level through a falling edge, and the fault has been eliminated;

[0133] Trigger control strategy switching. When the fault signal is detected to be low level, the system confirms that the fault has been cleared. After confirming that the fault has been cleared, the system triggers the control strategy switching mechanism and switches from the phase control strategy back 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 synchronous control link, the frequency will be locked at the grid frequency, the output active power will quickly converge to the active power reference value, and the system will 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 new energy units described in the present invention, the detailed implementation process of step S104 (fault clearing detection and strategy switching step) is as follows:

[0136] After a system fault occurs, the fault detection link will immediately generate and continuously send out a fault signal, which is usually a 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 link. PCC The amplitude of the fault is used as the main basis for judging whether the fault has been cleared.

[0137] Set a threshold (for example, 0.9pu), if the common point voltage U PCCIf the amplitude of the fault signal returns to above the threshold and remains above the threshold for a period of time (to ensure that it is not an instantaneous fluctuation), the fault is considered to have been cleared. When it is confirmed that the fault has been cleared, the fault detection link will change the state of the fault signal from the previous high level to the low level through a falling edge, indicating that the fault has been eliminated.

[0138] The system continuously monitors the state of the fault signal. Once the fault signal is detected to be low level, it is confirmed that the fault has been cleared. At this time, the system triggers the switching mechanism of the control strategy and prepares to switch from the current phase control strategy back to the virtual synchronous traditional control strategy.

[0139] During the switching process, the system will regenerate the virtual internal potential phase according to the virtual synchronous control link. This phase is no longer controlled by the previous phase locking link, but is dynamically adjusted according to the actual operating status of the system and the control algorithm of the virtual synchronous machine. At the same time, the system frequency continues to be locked at the grid frequency ω g , to ensure that the frequency does not shift during the switching process.

[0140] With the switching of the control strategy, the active power output by 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 completing the switching of the control strategy, the system will continue to monitor the changes in parameters 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 achieved the transition from the fault state to the stable state, improving the transient stability of the virtual synchronous new energy unit.

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

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

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

[0146] After confirming that the fault has been cleared, the phases that were forcefully locked during the previous fault are immediately cancelled.

[0147] The system switches from the phase control strategy back to the virtual synchronous control link, that is, the traditional virtual synchronous machine control strategy is restored, the internal potential phase is regenerated by the frequency integration, and the integral relationship between the phase and frequency is restored;

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

[0149] The active power output by 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 the present invention, the detailed implementation process of step S105 (restoring the traditional virtual synchronous control step) is as follows:

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

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

[0153] After confirming that the fault has been cleared, the system immediately cancels the internal potential phase that was previously 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, but will resume its normal dynamic adjustment mechanism.

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

[0155] After switching back to the traditional control strategy, the system frequency continues to remain at the grid frequency ω g Because during the fault period, the system has ensured the stability of the frequency through the frequency locking link, after switching back to the traditional control strategy, this stability can be maintained, avoiding the impact of sudden frequency changes on the system.

[0156] With the switching of control strategies and the recovery of system status, the active power output of the system will gradually converge to the active power reference value. This is one of the important signs that the system has recovered to a stable operating state, indicating that the system can operate stably according to the predetermined power output requirements.

[0157] After completing the above steps, the system enters the stable operation stage. At this time, the system's voltage, current, power and other parameters should be kept within the normal range, and the system can quickly respond and adjust to external load changes or small disturbances.

[0158] To summarize, step S105 achieves a smooth transition of the system from the phase control strategy to the traditional virtual synchronous control strategy after the fault is cleared through a series of operations such as real-time monitoring of the fault clearing status, canceling phase lock, switching back to the traditional control strategy, maintaining frequency stability, and ensuring active power convergence, thereby ensuring stable operation and rapid recovery of the system.

[0159] The present invention proposes a phase control strategy for improving the transient stability of virtual synchronous new energy units. Figure 2 As shown in the figure, the input and output quantities related to the four links are connected to obtain a complete phase control strategy block diagram. When the system is operating normally, a virtual synchronous control link (solid line frame) is adopted, the frequency is controlled by the active-frequency loop (1), and the internal potential phase is obtained by frequency integration (2). PCC When <0.9pu, the system is considered to have a fault. To avoid instability caused by excessive phase jump, the system switches to the phase control strategy (dashed box).

[0160]

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

[0162] After the fault disappears, the forced locked phase is canceled. At this time, the voltage rises, the fault signal jumps from 1 to 0, and the system switches back to the traditional control strategy. The phase jump is caused by the change in the topology structure. When the topology structure is restored, the phase immediately returns to the value before the fault, and the system returns to the operating state before the fault. After switching back to the traditional control strategy, the frequency is the control frequency during the fault, that is, the grid frequency. The output active power will not deviate greatly and will quickly converge to the active power reference value. The following introduces the contents of each module and its implementation method.

[0163] Fault detection link, through real-time measurement of common point voltage U PCC amplitude, monitor whether the current system has a fault. PCC <0.9pu, it is considered that a fault has occurred, and the fault signal changes from a low level to a high level after a rising edge.

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

[0165]

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

[0167] The phase locking link uses two triggers to lock the phase of the potential and terminal voltage at the moment of the fault. The fault signal generated by the fault detection link is introduced, and the trigger is triggered by the rising edge of the fault signal from 0 to 1, locking the θ E and θ U , thereby locking the difference between the two δ0(3-4).

[0168] δ0=θ E -θ U (4)

[0169] In the frequency control link, if no special control is taken on the frequency during the fault, the difference in active power will cause a large frequency deviation. After the fault is cleared, the traditional control strategy is switched back. The frequency deviation will affect the stability of active power. In order to achieve smooth switching of the control mode, the frequency needs to be controlled separately. During the fault, a control frequency is retained, which is equal to the grid frequency, to avoid excessive feedback of active power caused by frequency deviation after the fault is removed. Since there is no integral relationship between frequency and phase during the fault, the control of frequency is not inconsistent with the above control of phase.

[0170] The present invention proposes a phase control strategy for improving the transient stability of virtual synchronous new energy units. The specific flow chart is as follows Figure 6 shown.

[0171] Step 1: Use the fault detection link to detect whether a fault occurs and generate a fault signal. If a fault occurs, go to step 2; otherwise, go to step 6

[0172] Step 2: Use the phase locking link to lock the phase of the potential and terminal voltage at the moment of the fault, and calculate the phase difference δ0

[0173] Step 3: Use the phase calculation link to calculate the terminal voltage phase θ in real time 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: Use the fault detection link to determine whether the fault has been cleared. If the fault has been cleared, go to step 6; otherwise, go to step 3.

[0176] Step 6: Generate a virtual internal potential phase according to the virtual synchronous control link and resume normal operation.

[0177] Simulation conditions;

[0178]

[0179] Table 1 Simulation parameters

[0180] The fault is set to occur in 0.1s and removed in 4s. The transition resistance of the fault is 0.00625+j0.0065p.u., and the reactance on the system side is 0.03pu. Substituting the data into formula (2-3) for calculation, it can be obtained 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 operation area.

[0181] By referring to Figure 7 , Figure 8 as well as Fig. 9 Under the traditional control strategy, the three-phase short circuit under this condition causes the terminal voltage to drop and oscillate, the active power oscillates and produces negative values, the frequency increases, and the system becomes unstable. The instability here is the second type of instability. After the system fails, the phase jump is too large and enters the unstable operation area. The active power difference causes the frequency to increase and is always greater than the rated frequency. This is the fundamental reason for the power angle divergence and the continuous oscillation of active power.

[0182] This patent switches to the phase control strategy after 0.1s of fault, and the internal potential Locked in θ u +δ0, which prevents the power angle from diverging. The frequency is stable at 1p.u during the fault, and there is no integral relationship between phase and frequency; when the fault is cleared in 4s, it switches back to the traditional control strategy, at which time the frequency is the rated frequency, and the integral relationship between phase and frequency is restored. Therefore, smooth switching of frequency can be achieved. The oscillation during the active power fault is effectively suppressed, and it can quickly transition to a stable value after the fault occurs and after the fault is cleared. The terminal voltage is maintained at 0.67pu ​​during the fault, achieving transient stability.

[0183] The technical solution proposed in the present invention solves the problem that the potential phase during the fault period is no longer generated by frequency integration, but tracks the terminal voltage phase during the fault period, and the phase difference between the two is maintained at the value at the moment of the fault to prevent the divergence of the power angle. At the same time, it realizes smooth switching back to the virtual synchronization traditional control strategy after the fault, and locks the control frequency at the grid frequency ω during the fault period. g , in order to deal with the instability problem caused by excessive phase jump at the moment of fault:

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

[0185] Phase locking step: When the system detects a fault, the phase locking link is used to lock the internal potential at the moment of the fault (θ E ) and terminal voltage (θ U ) phase. Calculate and lock the phase difference δ0 between the two, that is, θ E =θ U +δ0.

[0186] Phase control and frequency locking steps: During a system fault, the terminal voltage phase θ is calculated in real time U , and lock the internal potential phase at θ U +δ0. At the same time, the frequency is controlled separately and locked at the grid frequency ω g .

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

[0188] Steps to restore normal operation: When the fault is cleared, the virtual internal potential phase is generated according to the virtual synchronous control link, the forced locked phase is canceled, and the system switches back to the traditional control strategy to restore normal operation. At this time, the voltage rises and the fault signal changes from high level to low level.

[0189] Prevent power angle divergence: By locking the internal potential and terminal voltage phase difference at the moment of fault, the power angle is kept from diverging during the fault period, 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. Since the frequency is locked at the grid frequency during the fault, the frequency will not deviate from the rated value after switching, avoiding drastic fluctuations in active power.

[0191] Dealing with excessive phase jumps at the moment of fault: By locking the phase difference at the moment of fault, the present invention can effectively deal with the instability problem caused by excessive phase jumps at the moment of fault, and improve the transient stability of the virtual synchronous new energy unit.

[0192] In summary, the technical solution of the present invention successfully solves the problem of controlling the potential phase during the fault period through precise phase locking, frequency control, and fault detection and clearing mechanism, and realizes smooth switching after the 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 new energy units, characterized in that: include: S101: Fault detection step, obtaining system data, using fault detection on the obtained data, and measuring the common point voltage U in real time PCC amplitude, monitor whether the system fails. If U PCC <0.9pu, the system is considered to have a fault, and the fault signal changes from a low level to a high level after a rising edge; S102: Phase locking step. When the system detects a fault, the phase locking link is used to lock the phase of the internal potential and the terminal voltage at the moment of the fault. The fault signal generated by the fault detection link is introduced. The trigger is triggered by the rising edge of the fault signal 0 to 1, and the internal potential phase θ at this moment is locked. E and terminal voltage phase θ U , calculate and lock the difference δ0 between the two; S103: Phase control and frequency locking step. During a system fault, the terminal voltage phase θ is calculated in real time using the phase calculation link. U , and lock the internal potential phase at θ U +δ0, and control the frequency separately to lock the frequency at the grid frequency ω g ; S104: Fault clearing detection step, continuing to use fault detection to determine whether the fault is cleared. If the fault is cleared, prepare to switch back to the traditional control strategy. Otherwise, continue to execute the phase control and frequency locking steps; S105: Step of resuming normal operation. When the fault is cleared, a virtual internal potential phase is generated according to the virtual synchronous control link, the forced locked phase is canceled, and the system switches back to the traditional control strategy to resume normal operation. The voltage rises, and the fault signal changes from a high level to a low level via 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 according to claim 1 is characterized in that: The step S101 includes: Using the fault detection link, the common point voltage U is measured in real time PCC The amplitude of Monitor whether the current system has a fault. The specific judgment basis is the common point voltage U PCC Is the amplitude less than 0.9pu? If U PCC If the amplitude is less than 0.9pu, the system is considered to have failed; If the fault signal changes from a low level to a high level through a rising edge, a fault has occurred in the system.

3. The phase control strategy for improving the transient stability of virtual synchronous new energy units according to claim 1 is characterized in that: The step S102 includes: By measuring the common point voltage U in real time PCC The amplitude is used to monitor whether the current system fails. If U PCC If the amplitude is less than 0.9pu, it is considered that the system has a fault, and the fault signal changes from a low level to a high level through a rising edge; When the fault signal changes from 0 to 1 on the rising edge, the phase locking link is enabled to lock the internal potential (θ E ) and terminal voltage (θ U )’s phase; At the same time as the phase lock is triggered, the phase difference δ0 between the internal potential and the terminal voltage is calculated. This is achieved by locking the θ E and θ U To achieve this, the phase difference δ0 is the difference between the two; During a fault, the phase of the internal potential is locked at the terminal voltage phase plus the phase difference δ0, that is, θ E =θ U +δ0.

4. The phase control strategy for improving the transient stability of virtual synchronous new energy units according to claim 1 is characterized in that: The step S103 includes: Real-time measurement of common point voltage U PCC If U PCC If the amplitude is less than 0.9pu, the system is considered to have failed; The fault signal changes from low level to high level through a rising edge. The trigger is used to lock the phase of the internal potential and terminal voltage at the moment of the fault. The trigger is triggered by the rising edge of the fault signal from 0 to 1, and the internal potential phase θ is locked at this moment. E and terminal voltage phase θ U , calculate the phase difference δ0 between the two; Extract the direct-axis and quadrature-axis components of the terminal voltage in real time, and calculate the current terminal voltage phase θ by a preset formula U , and the final terminal voltage phase is obtained through low-pass filtering; Lock the internal potential phase at θ U +δ0, the phase is stable during the fault; Lock the frequency to the grid frequency ω g , used to avoid frequency deviation after fault removal; Fault detection is used to determine whether the fault has been cleared. If the fault has been cleared, the locked phase is canceled and the control strategy is switched back to the traditional virtual synchronous control strategy. The voltage rises, the fault signal becomes a low level, and the system recovers.

5. The phase control strategy for improving the transient stability of virtual synchronous new energy units according to claim 1 is characterized in that: The step S104 includes: After a system failure occurs, the fault detection link will generate a fault signal; Determine whether the fault is cleared and measure the common point voltage U in real time through the fault detection link PCC The amplitude of If the common point voltage U PCC When the amplitude of is restored to above the set threshold, the fault is considered to have been cleared; At this time, the fault signal changes from a high level to a low level through a falling edge, and the fault has been eliminated; Trigger control strategy switching. When the fault signal is detected to be low level, the system confirms that the fault has been cleared. After confirming that the fault has been cleared, the system triggers the control strategy switching mechanism and switches from the phase control strategy back 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 synchronous control link, the frequency will be locked at the grid frequency, the output active power will quickly converge to the active power reference value, and the system will 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 according to claim 1, characterized in that: The step S105 includes: Real-time monitoring of common point voltage U PCC The amplitude of U PCC When it returns to the normal range, it is judged that the fault has been cleared; After confirming that the fault has been cleared, the phases that were forcefully locked during the previous fault are immediately cancelled. The system switches from the phase control strategy back to the virtual synchronous control link, that is, the traditional virtual synchronous machine control strategy is restored, the internal potential phase is regenerated by the frequency integration, and the integral relationship between the phase and frequency is restored; After switching back to the traditional control strategy, the frequency remains at the rated frequency; The active power output by the system will gradually converge to the active power reference value to ensure stable operation of the system.

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