Method and system for controlling transient stability under new energy networking control amplitude limiting condition

Abstract

The invention provides a method and a system for controlling transient stability under a new energy networking control amplitude limiting condition. The method comprises the following steps: judging transient synchronous stability of a networking type inverter under the amplitude limiting condition; if it is judged that the transient synchronous instability occurs in the network construction type inverter, the power grid voltage and the system impedance of the new energy network construction system after the fault is removed are calculated based on Thevenin equivalent parameters; obtaining a power characteristic curve of the new energy networking system according to the power grid voltage and the system impedance; and determining a residual power area when the new energy networking system is unstable according to the power characteristic curve, and determining an active power reference value of the adjusted new energy networking system based on the residual area. The problem of transient power angle instability caused by a new energy networking system in a current amplitude limiting link is solved, and the system stability is improved.

Description

Technical Field

[0001] This invention relates to the field of power system safety and stability analysis technology, specifically to a control method and system for transient stability under the control and limitation conditions of new energy grid construction. Background Technology

[0002] Grid-based inverters employ power synchronization strategies, enabling them to autonomously establish the amplitude and phase of port voltages and output power on demand, achieving synchronized operation with the grid. Even under weak grid conditions, they possess self-synchronization and stable operation capabilities. However, the inverter's overcurrent capacity is limited, necessitating the introduction of a current limiting mechanism. This mechanism significantly alters the transient synchronization process and dynamic characteristics of grid-based inverters. When current saturation occurs, the inverter's behavior tends to resemble that of a current source, leading to more complex synchronization and stability issues. Summary of the Invention

[0003] To address the aforementioned technical problems, this invention provides a control method for transient stability under the control limitation conditions of new energy grid construction, comprising:

[0004] The transient synchronization stability of a grid-connected inverter under limiting conditions is determined.

[0005] If it is determined that the grid-type inverter has experienced transient synchronous instability, the grid voltage and system impedance of the new energy grid system after the fault is cleared are calculated based on Thevenin equivalent parameters.

[0006] Based on the grid voltage and system impedance, the power characteristic curve of the new energy grid system is obtained;

[0007] The remaining power area when the new energy grid system becomes unstable is determined based on the power characteristic curve, and the adjusted active power reference value of the new energy grid system is determined based on the remaining area.

[0008] Furthermore, the transient synchronization stability of the grid-connected inverter under limiting conditions is determined, including:

[0009] Under the limiting condition, the virtual power angle curve is obtained by using the virtual power angle when the grid-type inverter current is saturated and the virtual power angle when the grid-type inverter current is not saturated.

[0010] Based on the virtual power angle curve, it is determined that when the acceleration area is greater than the deceleration area, the virtual power angle of the grid-type inverter is transient synchronous instability; when the deceleration area is greater than the acceleration area, the virtual power angle of the grid-type inverter is transient synchronous stability.

[0011] Furthermore, based on Thevenin equivalent parameters, the grid voltage and system impedance of the renewable energy grid system after fault clearance are calculated, including:

[0012] After a fault occurs and is disconnected in the renewable energy grid system, based on Thevenin equivalent parameters, the voltage E1 and current I1 at time t1 and the voltage E2 and current I2 at time t2 are measured. The grid voltage U and system impedance X after the fault is disconnected are then calculated using the following formulas.

[0013] E1-I1X=U

[0014] E2-I2X=U.

[0015] Furthermore, based on the grid voltage and system impedance, the power characteristic curve of the new energy grid system is obtained, including:

[0016] Discrete power characteristic curves are obtained using grid voltage U and system impedance X;

[0017] By fitting the power characteristic curve points, the power characteristic curve of the new energy grid system can be obtained.

[0018] Furthermore, determining the remaining power area of ​​the new energy grid system during instability based on the power characteristic curve includes:

[0019] Based on the power characteristic curve, discrete power characteristic curve points are obtained;

[0020] When the instability of the new energy grid system is determined, the remaining power area is obtained by using the least squares synthesis formula based on the discrete power characteristic curve points.

[0021] This invention also provides a control system for transient stability under the limiting conditions of new energy grid construction control, comprising:

[0022] The transient synchronization stability determination module is used to determine the transient synchronization stability of grid-connected inverters under limiting conditions.

[0023] The grid voltage and system impedance calculation module is used to calculate the grid voltage and system impedance of the new energy grid system after the fault is cleared based on Thevenin equivalent parameters if it is determined that the grid-type inverter has experienced transient synchronous instability.

[0024] The power characteristic curve acquisition module is used to obtain the power characteristic curve of the new energy grid system based on the grid voltage and system impedance.

[0025] The active power reference value adjustment module is used to determine the remaining power area when the new energy grid system becomes unstable based on the power characteristic curve, and to determine the adjusted active power reference value of the new energy grid system based on the remaining area.

[0026] Furthermore, the transient synchronization stability determination module includes:

[0027] The virtual power angle curve acquisition submodule is used to obtain the virtual power angle curve under limiting conditions by using the virtual power angle when the grid-type inverter current is saturated and the virtual power angle when the grid-type inverter current is not saturated.

[0028] The transient state determination submodule is used to determine, based on the virtual power angle curve, that when the acceleration area is greater than the deceleration area, the virtual power angle of the grid-type inverter is transiently synchronously unstable; and when the deceleration area is greater than the acceleration area, the virtual power angle of the grid-type inverter is transiently synchronously stable.

[0029] Furthermore, the grid voltage and system impedance calculation module includes:

[0030] The voltage and impedance calculation submodule is used to measure the voltage E1 and current I1 at time t1 and the voltage E2 and current I2 at time t2 of a fault in a renewable energy grid system after the fault is cleared, based on Thevenin equivalent parameters. The grid voltage U and system impedance X after the fault is cleared are then calculated using the following formulas.

[0031] E1-I1X=U

[0032] E2-I2X=U.

[0033] Furthermore, the active power reference value adjustment module includes:

[0034] The curve point acquisition submodule is used to obtain discrete power characteristic curve points based on the power characteristic curve.

[0035] The residual power area calculation submodule is used to calculate the residual power area by using the least squares synthesis formula based on discrete power characteristic curve points when the instability of the new energy grid system is determined.

[0036] The present invention also provides a computer-readable storage medium having a computer program stored thereon, wherein when the computer program is executed, it implements the control method for transient stability under the control limit conditions of new energy grid construction as described in any one of the preceding claims.

[0037] This invention provides a control method and system for transient stability under current limiting conditions in new energy grid construction. By analyzing the trend of the speed difference relative to the power angle change, the transient stability state of the system is determined in real time. When the system loses power angle stability, the remaining acceleration area is calculated, and the adjustment amount of active power is determined accordingly. This solves the problem of transient power angle instability caused by current limiting in new energy grid construction systems, thus improving system stability. Attached Figure Description

[0038] Figure 1 This is a flowchart illustrating a control method for transient stability under the control limit conditions of new energy grid construction, provided by an embodiment of the present invention.

[0039] Figure 2 This refers to the virtual power angle transient stability of the inverter involved in the embodiments of the present invention;

[0040] Figure 3 This is the overall process of real-time emergency control involved in the embodiments of the present invention;

[0041] Figure 4 This refers to the transient power angle curve of the network construction system involved in the embodiments of the present invention;

[0042] Figure 5 This is a schematic diagram of a control system for transient stability under the control limit conditions of new energy grid construction, provided by an embodiment of the present invention. Detailed Implementation

[0043] Numerous specific details are set forth in the following description to provide a full understanding of the invention. However, the invention can be practiced in many other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0044] To address the issue of transient instability in grid-connected inverters for new energy applications under current limiting conditions, this invention provides a control method for transient stability under current limiting conditions in grid-connected new energy applications, comprising the following steps:

[0045] Step S101: Determine the transient synchronization stability of the grid-type inverter under the limiting condition.

[0046] First, it is necessary to understand the model of the grid-type control converter, including the system topology of the grid-type converter and its control strategy. By understanding these, we can understand the virtual power angle characteristic equation of the inverter, and thus perform transient synchronous stability analysis on the grid-type converter.

[0047] When the power grid experiences large disturbances such as short circuits, a significant short-circuit current is generated. Since overcurrent can damage the inverter, the inverter's output current is often limited in the control system. The analysis of the limiting circuit consists of three parts: the virtual power angle characteristics under inverter saturation, the transient stability mechanism analysis of the inverter's virtual power angle, and the transient stability analysis of the acceleration / deceleration area. Specifically, under limiting conditions, virtual power angle curves are obtained by comparing the virtual power angles of the grid-connected inverter when the current is saturated and when the current is not saturated. Based on these curves, it is determined that when the acceleration area is greater than the deceleration area, the virtual power angle of the grid-connected inverter is in transient synchronous instability; when the deceleration area is greater than the acceleration area, the virtual power angle of the grid-connected inverter is in transient synchronous stability.

[0048] (1) Virtual power angle characteristics under inverter saturation

[0049] Once the current saturates, due to the current-priority limiting mechanism of the d-axis, the d-axis current will gradually increase to I. max The q-axis current will gradually decrease to zero. The active power output of the GFM-VSC will also change under current-limited operation. Due to I... max Due to limitations, the maximum value of the limiting curve is less than the maximum value of the normal operation curve. Therefore, when the GFM-VSC is in limiting operation, the system may not have a stable operating point, requiring timely fault isolation to ensure stable system operation. When the grid voltage drop is deep, the system will not have a stable operating point.

[0050] (2) Analysis of the transient stability mechanism of the virtual power angle of the inverter

[0051] like Figure 2 As shown, when the current is not saturated, the inverter operates on the unsaturated power angle curve; when the current is saturated, the inverter operates on the saturated curve. The transition between the two states is the switching of the virtual power angle curve, that is, the inverter's operating point switches from the unsaturated virtual power angle curve to the saturated virtual power angle curve.

[0052] (3) Transient stability analysis of acceleration and deceleration area

[0053] The equal area rule can be used to determine whether the system will experience virtual power angle instability. When the acceleration area is greater than the deceleration area, the virtual power angle of the virtual synchronizer will experience transient instability; when the deceleration area is greater than the acceleration area, the virtual power angle of the virtual synchronizer will experience transient stability.

[0054] Step S102: If it is determined that the grid-type inverter has experienced transient synchronous instability, the grid voltage and system impedance of the new energy grid system after the fault is cleared are calculated based on Thevenin equivalent parameters.

[0055] After a system failure, the network may change, and the maximum operating DC power is related to system parameters. Therefore, it is necessary to estimate the Thevenin equivalent parameters after the failure. Here, a Thevenin estimation method suitable for large disturbances is adopted. This method first reduces the impact of system-side changes by screening measurement data with large current variations, and then uses the overall least squares method for impedance estimation.

[0056] After a fault occurs and is disconnected in the renewable energy grid system, based on Thevenin equivalent parameters, the voltage E1 and current I1 at time t1 and the voltage E2 and current I2 at time t2 are measured. The grid voltage U and system impedance X after the fault is disconnected are then calculated using the following formulas.

[0057] E1-I1X=U

[0058] E2-I2X=U.

[0059] Step S103: Obtain the power characteristic curve of the new energy grid system based on the grid voltage and system impedance.

[0060] Discrete power characteristic curves are obtained using grid voltage U and system impedance X; by fitting these power characteristic curves, the power characteristic curve of the new energy grid system is obtained.

[0061] Step S104: Determine the remaining power area when the new energy grid system becomes unstable based on the power characteristic curve, and determine the adjusted active power reference value of the new energy grid system based on the remaining area.

[0062] Based on the power characteristic curve, discrete power characteristic curve points are obtained. When it is determined that the new energy grid system is unstable, the remaining power area is obtained by using the least squares synthesis formula with the discrete power characteristic curve points. Specifically, the transient stability of the power grid is identified in real time by the trend of the change in the relative power angle of the speed difference. When it is determined that the system will lose power angle stability, the remaining acceleration area is calculated based on the concept of relative kinetic energy in the two-machine system.

[0063] Assume the power curve of this image in a single-machine infinite system is as follows:

[0064]

[0065] Calculate the current and voltage values ​​at the generator port of the grid at time t and time t+1. Using formula (2), the voltage and impedance values ​​of the grid can be obtained, and thus the power characteristic curve of the equivalent system can be obtained.

[0066]

[0067] In a practical system, if the mechanical power of all generators can be measured in real time, discrete power characteristic curves can be obtained according to equation (2). Starting from the fault clearing time, P is calculated at each time point. e By obtaining a series of discrete points of the power characteristic curve, when it is identified that the system will lose stability, the remaining deceleration area can be estimated by using all the existing discrete points in the form of a least squares synthesis, providing a basis for adjusting the active power reference value of the network structure.

[0068] Traditional calculation methods use a data window over a period of time to predict the power characteristic curve because they require comparing acceleration and deceleration areas to determine system stability. This method uses all available data to fit the power characteristic curve. However, under the influence of various factors, this method is only an approximation to a certain extent, and the purpose of fitting is to estimate the remaining deceleration area. In emergency control, reducing the active power reference value not only reduces mechanical power input but also affects the system impedance, making it difficult to obtain an accurate power characteristic curve. Therefore, a cyclic monitoring and control approach is adopted to continuously evaluate system operation. If a single tripping control fails to stabilize the system, another tripping control is implemented.

[0069] Specific application examples

[0070] based on Figure 3 The real-time emergency control process and the single-machine infinite bus equivalent system were used to verify the effectiveness of the proposed method, and the grid current limit I was set. max =0.26, P ref =0.23, during the fault the grid voltage drops to 0.6, X g =1.5.

[0071] After a system fault occurs and is cleared, the fault voltage E1 and current I1 at time t1 and E2 and I2 at time t2 are measured in real time. The grid voltage U and system impedance X after the fault is cleared are then calculated using the following formulas.

[0072] formula:

[0073] E1-I1X=U

[0074] E2-I2X=U

[0075] Therefore, the system impedance and the grid voltage after fault recovery can be obtained through the formula, and the virtual power angle curve of the system can be plotted. After analysis, it is identified that the system will lose stability at 3.1s. At this time, the remaining acceleration area is 0.0833, and the fitted remaining deceleration area is 0.08218.

[0076] Figure 4 For predicting curves, such as Figure 4 As shown, at this time, S1-S2==0.08237.S3+S4=0.08218<0.08237, so the system loses stability.

[0077] The angular velocity at point O is ω = 1.0013.

[0078] The following can be obtained using the relative kinetic energy formula:

[0079] S remain =0.0833

[0080] It can be seen that the remaining acceleration area obtained by the relative kinetic energy formula is basically equal to the verified remaining acceleration area.

[0081] Therefore, we obtain ΔPm = 0.012, so we decide to adjust Pre to decrease by 0.012 at 3.2s. By adopting the measure of adjusting Pre in response, we can prevent the accident from escalating further.

[0082] Based on the same inventive concept, this invention also provides a control system 500 for transient stability under the limiting conditions of new energy grid construction control, such as... Figure 5 As shown, it includes:

[0083] The transient synchronization stability determination module 510 is used to determine the transient synchronization stability of the grid-connected inverter under limiting conditions.

[0084] The grid voltage and system impedance calculation module 520 is used to calculate the grid voltage and system impedance of the new energy grid system after the fault is cleared based on Thevenin equivalent parameters if it is determined that the grid-type inverter has experienced transient synchronous instability.

[0085] The power characteristic curve acquisition module 530 is used to obtain the power characteristic curve of the new energy grid system based on the grid voltage and system impedance.

[0086] The active power reference value adjustment module 540 is used to determine the remaining power area when the new energy grid system becomes unstable based on the power characteristic curve, and to determine the adjusted active power reference value of the new energy grid system based on the remaining area.

[0087] Furthermore, the transient synchronization stability determination module includes:

[0088] The virtual power angle curve acquisition submodule is used to obtain the virtual power angle curve under limiting conditions by using the virtual power angle when the grid-type inverter current is saturated and the virtual power angle when the grid-type inverter current is not saturated.

[0089] The transient state determination submodule is used to determine, based on the virtual power angle curve, that when the acceleration area is greater than the deceleration area, the virtual power angle of the grid-type inverter is transiently synchronously unstable; and when the deceleration area is greater than the acceleration area, the virtual power angle of the grid-type inverter is transiently synchronously stable.

[0090] Furthermore, the grid voltage and system impedance calculation module includes:

[0091] The voltage and impedance calculation submodule is used to measure the voltage E1 and current I1 at time t1 and the voltage E2 and current I2 at time t2 of a fault in a renewable energy grid system after the fault is cleared, based on Thevenin equivalent parameters. The grid voltage U and system impedance X after the fault is cleared are then calculated using the following formulas.

[0092] E1-I1X=U

[0093] E2-I2X=U.

[0094] Furthermore, the active power reference value adjustment module includes:

[0095] The curve point acquisition submodule is used to obtain discrete power characteristic curve points based on the power characteristic curve.

[0096] The residual power area calculation submodule is used to calculate the residual power area by using the least squares synthesis formula based on discrete power characteristic curve points when the instability of the new energy grid system is determined.

[0097] This invention provides a control method and system for transient stability under current limiting conditions in renewable energy grid construction. By analyzing the virtual power angle characteristics under inverter current saturation, the transient stability mechanism of the inverter's virtual power angle, and the acceleration / deceleration area of ​​the power angle curve, combined with real-time estimation using Thevenin equivalent parameters, and finally utilizing the relative kinetic energy method, a generator tripping measure is taken to effectively increase the deceleration area of ​​the power angle curve, ensuring real-time system stability. This invention does not rely on traditional power system component modeling and operation methods; it can be implemented solely based on the system's dynamic response curve, making it suitable for various complex operating conditions and fault scenarios. The calculation process only requires measured generator power angle and speed data, offering advantages such as low computational load, fast response, and flexible deployment. This control scheme helps prevent further deterioration of the system state, reduces the risk of large-scale power outages, and solves the transient power angle instability problem caused by current limiting in renewable energy grid construction systems.

[0098] Those skilled in the art will understand that embodiments of the present invention can be provided as methods, systems, or computer program products. Therefore, the present invention can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present invention can take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0099] This invention is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart illustrations and / or block diagrams.Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0100] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0101] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0102] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the scope of the claims of the present invention.

Claims

1. A control method for transient stability under new energy network control limiting conditions, characterized in that, The application relates to a method for determining transient synchronous stability of a grid-connected inverter under an amplitude limiting condition. If it is determined that the grid-connected inverter is in transient synchronous instability, the grid voltage and system impedance of the new energy grid-connected system after fault removal are calculated based on Thevenin equivalent parameters. According to the grid voltage and system impedance, a power characteristic curve of the new energy grid-connected system is obtained. According to the power characteristic curve, the residual power area of the new energy grid-connected system when instability occurs is determined, and the adjusted active power reference value of the new energy grid-connected system is determined based on the residual area. The method for determining transient synchronous stability of a grid-connected inverter under an amplitude limiting condition comprises the following steps.

2. The method of claim 1, wherein, Under the amplitude limiting condition, a virtual power angle curve is obtained through a virtual power angle when the grid-connected inverter current is saturated and a virtual power angle when the grid-connected inverter current is not saturated. Based on the virtual power angle curve, when the acceleration area is greater than the deceleration area, the virtual power angle of the grid-connected inverter is in transient synchronous instability; and when the deceleration area is greater than the acceleration area, the virtual power angle of the grid-connected inverter is in transient synchronous stability. The method for calculating the grid voltage and system impedance of the new energy grid-connected system after fault removal based on Thevenin equivalent parameters comprises the following steps.

3. The method of claim 1, wherein, After the new energy grid-connected system is faulted and removed, the voltage E1 and current I1 at t1 and the voltage E2 and current I2 at t2 are measured based on Thevenin equivalent parameters, and the grid voltage U and system impedance X after fault removal are solved through the following formula, E1-I1X=U E2-I2X=U. The method for obtaining the power characteristic curve of the new energy grid-connected system according to the grid voltage and system impedance comprises the following steps.

4. The method according to claim 1 or 3, characterized in that, The discrete power characteristic curve points are obtained through the grid voltage U and system impedance X. The power characteristic curve of the new energy grid-connected system is obtained through fitting the power characteristic curve points. The method for determining the residual power area of the new energy grid-connected system when instability occurs according to the power characteristic curve comprises the following steps.

5. The method according to claim 1 or 3, characterized in that, The discrete power characteristic curve points are obtained according to the power characteristic curve. When it is determined that the new energy grid-connected system is unstable, the discrete power characteristic curve points are used to synthesize the residual power area by using the least square method. The application relates to a method for determining transient synchronous stability of a grid-connected inverter under an amplitude limiting condition.

6. A control system for transient stability under new energy network control limiting conditions, characterized in that, A transient synchronous stability determination module is used for determining transient synchronous stability of a grid-connected inverter under an amplitude limiting condition. A grid voltage and system impedance calculation module is used for calculating the grid voltage and system impedance of the new energy grid-connected system after fault removal based on Thevenin equivalent parameters if it is determined that the grid-connected inverter is in transient synchronous instability. A power characteristic curve obtaining module is used for obtaining the power characteristic curve of the new energy grid-connected system according to the grid voltage and system impedance. An active power reference value adjustment module is used for determining the residual power area of the new energy grid-connected system when instability occurs according to the power characteristic curve, and determining the adjusted active power reference value of the new energy grid-connected system based on the residual area. The transient synchronous stability determination module comprises the following steps.

7. The system of claim 6, wherein, A virtual power angle curve obtaining sub-module is used for obtaining a virtual power angle curve through a virtual power angle when the grid-connected inverter current is saturated and a virtual power angle when the grid-connected inverter current is not saturated under the amplitude limiting condition. ​ The transient state judgment submodule is configured to determine, based on the virtual power angle curve, that the virtual power angle of the grid-forming inverter is transiently unstable when the acceleration area is greater than the deceleration area, and that the virtual power angle of the grid-forming inverter is transiently stable when the deceleration area is greater than the acceleration area.

8. The system of claim 6, wherein, The power grid voltage and system impedance calculation module comprises: The voltage and impedance solving submodule is configured to, after the new energy grid-forming system is subjected to a fault and the fault is removed, solve the power grid voltage U and the system impedance X after the fault is removed based on the Thevenin equivalent parameters, the voltage E1 and the current I1 at time t1, and the voltage E2 and the current I2 at time t2 of the fault, by the following formulas: E1-I1X=U E2-I2X=U.

9. The system of claim 6, wherein, The active power reference value adjustment module comprises: The curve point obtaining submodule is configured to obtain discrete power characteristic curve points according to the power characteristic curve. The residual power area calculation submodule is configured to, when it is determined that the new energy grid-forming system is unstable, calculate the residual power area by using the discrete power characteristic curve points and a least square method synthesis formula.

10. A computer-readable storage medium, characterized in that, The computer program is stored thereon, and when the computer program is executed, the control method for transient stability under a new energy grid-forming control limiting condition is implemented.

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