A new energy multi-feed-in system whole-process transient overvoltage quantitative calculation method based on a wide-band impedance model and related equipment

Abstract

This invention belongs to the field of power system transient analysis technology. It discloses a method and related equipment for the quantitative calculation of transient overvoltage in a new energy multi-infeed system based on a wideband impedance model. A wideband impedance model of the voltage support equipment is established, incorporating its impedance characteristics across the entire frequency band into transient overvoltage analysis. Based on this wideband impedance model, a frequency domain transient overvoltage analysis model considering the dynamic characteristics of the entire system across the entire frequency band is established. This allows the characterization of the system's dynamic characteristics to extend beyond a single frequency band, covering the low, medium, and high frequency ranges. A mapping relationship between the frequency domain model and the time domain transient overvoltage is established. The entire process voltage fluctuation curve is calculated and peak values ​​are extracted based on the reactive current injection process at the grid connection point before and after the fault and the voltage fluctuation at the fault node. This allows for a complete characterization of the voltage dynamic evolution characteristics throughout the entire process, from the steady state before the fault, the transient state during the fault, and the recovery process after the fault is cleared, rather than simply estimating a single peak value.

Description

Technical Field

[0001] This invention belongs to the field of power system transient analysis technology, specifically a quantitative calculation method and related equipment for full-process transient overvoltage of new energy multi-infeed systems based on a wideband impedance model. Background Technology

[0002] With the continuous growth of new energy grid connection, the power system exhibits the "dual high" characteristics of high proportion of new energy and high proportion of power electronic equipment connected to the grid. The grid connection of a large number of new energy units adopting grid-following control strategies has led to insufficient voltage support capacity of the system. The transient overvoltage generated after fault clearance seriously threatens the safe and stable operation of the system. The quantitative calculation of transient overvoltage is a key step in assessing the operational risk of the system.

[0003] Existing transient overvoltage quantification methods aim to estimate peak values, lack analysis of voltage response throughout the fault process, fail to account for the dynamic characteristics of the system across the entire frequency band, and do not consider the access scenarios of voltage support equipment. They cannot meet the needs of high-proportion new energy power systems for accurate transient overvoltage analysis.

[0004] Understanding the mechanism of transient overvoltage generation is fundamental to quantitative calculations. Current mainstream view holds that during a system fault, renewable energy sources trigger low-voltage ride-through control and inject reactive current into the system. After the fault is cleared, due to the delay in low-voltage ride-through control, the system recovers to its pre-fault voltage, but a reactive power surplus remains, causing the voltage to continue to rise. Based on this mechanism, existing transient overvoltage calculation methods treat renewable energy sources as equivalent current source models and then estimate the peak transient overvoltage based on the voltage-current relationship. In engineering applications, this method can quickly provide estimates of the overvoltage peak value, offering a preliminary basis for assessing system safety and stability risks.

[0005] The existing methods described above have inherent limitations. First, they only estimate the peak value of transient overvoltages, failing to provide voltage fluctuation curves for the entire process before, during, and after a fault, lacking a complete characterization of the dynamic voltage evolution during transient processes and thus hindering systematic analysis of overvoltage suppression strategies. Second, with a high proportion of renewable energy grid integration, the sending-end grid exhibits weak support characteristics, requiring the configuration of various types of voltage support equipment, such as distributed synchronous condensers, to enhance the system's voltage support capability. After the grid connection of various types of power electronic equipment and voltage support equipment, the system's dynamic characteristics cover multiple frequency bands, including low, medium, and high. However, existing methods, based on power frequency phasors or simplified dynamic models to establish voltage-current relationships, struggle to account for the impact of the system's full-frequency dynamic characteristics on transient overvoltages. Furthermore, the current source equivalent models of existing methods cannot reflect the impedance characteristics of voltage support equipment and its broadband interaction with the grid. Therefore, these methods are inapplicable when distributed synchronous condensers and other equipment are integrated into the system. Summary of the Invention

[0006] This invention provides a method and related equipment for quantifying and calculating transient overvoltages throughout the entire process of a new energy multi-infeed system based on a wideband impedance model. It solves the problems that existing transient overvoltage quantification methods cannot take into account the dynamic characteristics of the system across the entire frequency band and are not applicable to new energy multi-infeed systems with voltage support equipment.

[0007] To achieve the above objectives, the present invention provides the following technical solution: A quantitative calculation method for transient overvoltage throughout the entire process of a new energy multi-infeed system based on a wideband impedance model includes the following steps: Establish a broadband impedance model for voltage-supported equipment; Based on the aforementioned wideband impedance model, a frequency domain transient overvoltage analysis model considering the dynamic characteristics of the system across the entire frequency band is established. Establish the mapping relationship between the frequency domain transient overvoltage analysis model and the time domain transient overvoltage; Based on the reactive current injection process of the new energy grid connection point before and after the fault and the voltage fluctuation of the fault node, the voltage fluctuation curve of the new energy grid connection point during the entire fault process is calculated based on the mapping relationship, and the transient overvoltage peak value is extracted from the voltage fluctuation curve.

[0008] Preferably, the voltage support device is a distributed synchronous condenser; the establishment of a broadband impedance model for the voltage support device includes: Linearization and Laplace transform of the voltage and flux linkage equations of the distributed synchronous condenser body are performed to obtain the small-signal voltage-current relationship. Combining the rotor motion equation and the electromagnetic torque equation, where the mechanical torque input is zero, the flux disturbance term is derived from the voltage equation and the flux equation. By combining the small-signal voltage-current relationship, the rotor motion equation, and the electromagnetic torque equation, and eliminating intermediate variables, the impedance model of the distributed synchronous condenser in the rotor dq coordinate system is obtained.

[0009] Preferably, establishing a broadband impedance model for voltage-supported equipment further includes: The impedance model in the rotor dq coordinate system is transformed to the common synchronous dq coordinate system. The influence of small disturbances on the transformation angle is considered during the transformation. Then, the impedance in the common synchronous dq coordinate system is transformed to the grid voltage-oriented dq coordinate system to obtain the broadband impedance model of the distributed synchronous condenser.

[0010] Preferably, establishing a frequency domain transient overvoltage analysis model includes: The fault point is treated as a virtual node and included in the node admittance matrix calculation to form a partial node admittance matrix of the AC power grid. The node admittance matrix is ​​corrected based on the impedance of the voltage support equipment connected to each node; The modified node admittance matrix is ​​divided into blocks according to the new energy feed-in nodes, fault nodes and passive nodes. After Kron reduction simplification, the current and voltage relationship of the new energy grid connection point and the fault node is obtained. By swapping the positions of the input and output variables in the current-voltage relationship and performing linearization, a frequency domain transient overvoltage analysis model is obtained.

[0011] Preferably, establishing the mapping relationship between the frequency domain transient overvoltage analysis model and the time domain transient overvoltage includes: The reactive current injection process at the grid connection point and the voltage fluctuation at the fault node are abstracted as a step process, and the frequency domain fluctuation of the grid connection point voltage is calculated in combination with the frequency domain transient overvoltage analysis model. The mapping relationship between the frequency domain transient overvoltage analysis model and the time domain transient overvoltage is established by combining the inverse Laplace transform; When performing the inverse Laplace transform on the frequency domain fluctuation, the imaginary axis is selected as the integration path, and the mapping relationship between the frequency domain model and the time domain transient overvoltage is obtained by combining the discrete summation method.

[0012] Preferably, the voltage fluctuation curve of the new energy grid connection point during the entire fault process includes: The entire fault process is decomposed into multiple events, which include at least the voltage drop at the fault node, reactive current injection at the grid connection point, voltage recovery at the fault node, and cessation of reactive current injection. The magnitude of the voltage recovery at the fault node is determined as follows: the voltage recovery at the moment of fault clearance is calculated by combining the fault node injected current vector of the previous sampling point before fault clearance with the boundary condition that the node injected current is set to zero at the moment of fault clearance, and used as the input variable for the fault node voltage recovery event. Based on the occurrence time of each event, the output vector corresponding to each event is calculated according to the mapping relationship, and the voltage increment of the grid connection point during the entire fault process is obtained according to the principle of time shift and linear superposition. Extract the transient overvoltage peak from the d-axis and q-axis components of the voltage fluctuation at the grid connection point after fault clearance.

[0013] A quantitative calculation system for transient overvoltage throughout the entire process of a new energy multi-infeed system based on a wideband impedance model, comprising: Impedance Model Building Module: Used to build broadband impedance models for voltage-supported devices; Analysis model building module: used to build a frequency domain transient overvoltage analysis model that takes into account the dynamic characteristics of the system across the entire frequency band, based on the wideband impedance model; Mapping Relationship Establishment Module: Used to establish the mapping relationship between the frequency domain transient overvoltage analysis model and the time domain transient overvoltage; Voltage peak extraction module: It is used to calculate the voltage fluctuation curve of the new energy grid connection point during the entire fault process based on the mapping relationship, according to the reactive current injection process of the new energy grid connection point before and after the fault and the voltage fluctuation of the fault node, and extract the transient overvoltage peak from the voltage fluctuation curve.

[0014] A computer device includes a memory, a processor, and a computer program stored in the memory, wherein the processor executes the computer program to implement the steps of a method for quantifying and calculating transient overvoltages throughout the entire process of a new energy multi-infeed system based on a wideband impedance model.

[0015] A computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps of a method for quantifying and calculating transient overvoltages throughout the entire process of a new energy multi-infeed system based on a wideband impedance model.

[0016] A computer program product includes a computer program that, when executed by a processor, implements the steps of a method for quantifying and calculating transient overvoltages throughout the entire process of a new energy multi-infeed system based on a wideband impedance model. Compared with existing technologies, the present invention has the following advantages: The present invention provides a method for quantifying and calculating transient overvoltages throughout the entire process of a new energy multi-infeed system based on a wideband impedance model. By establishing a wideband impedance model for voltage support equipment, the impedance characteristics of the voltage support equipment are incorporated into transient overvoltage analysis across the entire frequency band. This allows for the effective handling of access scenarios for various types of voltage support equipment, such as distributed synchronous condensers, overcoming the limitation that existing current source equivalent models cannot reflect the wideband interaction of voltage support equipment. Based on the wideband impedance model, a frequency domain transient overvoltage analysis model considering the dynamic characteristics of the system across the entire frequency band is established, enabling the system's dynamic characteristics to be more accurately analyzed. The characterization is not limited to a single frequency band but covers the entire low, medium, and high frequency range, solving the problem that existing methods based on power frequency phasors or simplified dynamic models cannot account for the dynamic characteristics of the entire system across the entire frequency band. It establishes a mapping relationship between the frequency domain model and the time domain transient overvoltage, enabling the time domain response of transient overvoltage to be directly solved from the frequency domain model, providing a connecting means for calculating the voltage fluctuation curve of the entire process. It calculates the voltage fluctuation curve of the entire process and extracts the peak value based on the reactive current injection process of the grid connection point before and after the fault and the voltage fluctuation of the fault node, so that the voltage dynamic evolution characteristics of the steady state before the fault, the transient state during the fault, and the recovery process after the fault are fully characterized, rather than just estimating a single peak value. Attached Figure Description

[0017] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a flowchart of a method for quantifying and calculating transient overvoltages throughout the entire process of a new energy multi-infeed system based on a wideband impedance model, according to an embodiment of the present invention. Figure 2 This is a block diagram of the self-excitation adjustment according to an embodiment of the present invention; Figure 3 This is a topology diagram of the power plant sending-end system in an embodiment of the present invention, where a is the topology diagram of the new energy multi-infeed system, b is the topology diagram of the power plant, and c is the equivalent circuit diagram of the power plant. Figure 4 This is a new energy delivery system according to an embodiment of the present invention; Figure 5 The transient overvoltage calculation curves under different reactive current injections under symmetrical faults are shown in the embodiments of the present invention. Figure 6 This is a topology diagram of an IEEE 39-node system according to an embodiment of the present invention; Figure 7 The above are the transient overvoltage calculation curves for each grid connection point in the IEEE 39 system according to an embodiment of the present invention. Figure 8 This is a block diagram of a transient overvoltage quantification calculation system for a new energy multi-infeed system based on a wideband impedance model, according to an embodiment of the present invention. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0020] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0021] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0022] To enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings.

[0023] This invention proposes a quantitative calculation method for transient overvoltage throughout the entire process of a new energy multi-infeed system based on a wideband impedance model. In a new energy multi-infeed system with distributed synchronous condensers as voltage support equipment, a frequency domain transient overvoltage analysis model is constructed by establishing a wideband impedance model of the voltage support equipment. This model can take into account the dynamic characteristics of the system across the entire frequency band, achieving a high-precision characterization of the fault process. Then, a mapping relationship between the frequency domain model and the time domain transient overvoltage is established, ultimately constructing a method for calculating the entire process of transient overvoltage based on the wideband impedance model. This method can calculate the voltage fluctuation curves of the entire process before and after a system fault, taking into account the dynamic characteristics of the voltage support equipment and the entire system across the entire frequency band.

[0024] like Figure 1 As shown, it includes the following steps: S1: Establish a broadband impedance model for voltage support equipment; S2: Based on the aforementioned wideband impedance model, establish a frequency domain transient overvoltage analysis model that takes into account the dynamic characteristics of the system across the entire frequency band; S3: Establish the mapping relationship between the frequency domain transient overvoltage analysis model and the time domain transient overvoltage; S4: Based on the reactive current injection process of the new energy grid connection point before and after the fault and the voltage fluctuation of the fault node, calculate the voltage fluctuation curve of the new energy grid connection point throughout the fault process based on the mapping relationship, and extract the transient overvoltage peak value from the voltage fluctuation curve.

[0025] By establishing a broadband impedance model for voltage support equipment, the impedance characteristics of the voltage support equipment are incorporated into transient overvoltage analysis across the entire frequency band. This allows for the effective handling of various access scenarios for voltage support equipment, such as distributed synchronous condensers, overcoming the limitation of existing current source equivalent models that cannot reflect the broadband interaction of voltage support equipment. Based on the broadband impedance model, a frequency domain transient overvoltage analysis model considering the dynamic characteristics of the system across the entire frequency band is established. This allows the characterization of the system's dynamic characteristics to extend beyond a single frequency band, covering the low, medium, and high frequency ranges. This solves the problem that existing methods based on power frequency phasors or simplified dynamic models cannot adequately consider the dynamic characteristics of the system across the entire frequency band. A mapping relationship between the frequency domain model and the time domain transient overvoltage is established, enabling the time domain response of transient overvoltage to be directly solved from the frequency domain model, providing a connecting means for calculating the voltage fluctuation curve throughout the entire process. The voltage fluctuation curve throughout the entire process is calculated and the peak value is extracted based on the reactive current injection process at the grid connection point before and after the fault and the voltage fluctuation at the fault node. This allows for a complete characterization of the voltage dynamic evolution characteristics throughout the entire process, including the steady state before the fault, the transient state during the fault, and the recovery process after the fault is cleared, rather than simply estimating a single peak value.

[0026] Detailed steps include: (1) Impedance modeling of distributed synchronous condensers The voltage equation for the distributed synchronous condenser is shown below: (1) In the formula: for d Shaft voltage; Stator resistance; for d shaft current; The rotor's electric angular velocity; For stator q Shaft flux linkage; It is a differential operator; For stator d Axial magnetic flux; for q Shaft voltage; for q shaft current; This is the excitation voltage; The resistance of the excitation winding; It is the excitation current; This refers to the flux linkage of the excitation winding; the other windings are similar, where " "express d Shaft damping winding, " and" "express q There are two damping windings on the shaft, and all quantities are per-unit values.

[0027] The flux linkage equation is as follows: (2) In the formula: for d Shaft synchronous inductor; for d Armature reaction mutual inductance; for q Shaft synchronous inductor; for q Armature reaction mutual inductance; The self-inductance of the excitation winding; Excitation winding and d Mutual inductance of shaft damping windings; for d Self-inductance of shaft damping winding; for q The self-inductance of the first damping winding of the shaft, for q The self-inductance of the second damping winding of the shaft.

[0028] Based on the voltage equation and flux linkage equation of the distributed synchronous condenser, linearization and Laplace transform are performed to obtain: (3) Summarized as follows: (4) In the distributed synchronous condenser speed control process, only the rotor motion equation is considered. The rotor motion equation is also linearized and subjected to Laplace transform to obtain the following: (5) For distributed synchronous condensers, the mechanical torque input is zero, so the small-signal interference of the mechanical torque component can be ignored. The electromagnetic torque output by the motor can be expressed using flux linkage and current, as follows: (6) The flux perturbation term can be derived from equations (1) and (2): (7) in, (8) Summarized as follows: (9) Considering that the excitation circuit of the distributed synchronous condenser is self-excited and regulated, such as Figure 2 As shown, the transfer function of the excitation element can be obtained as follows: (10) Linearization and Laplace transform of the above equations yield the following: (11) Summarized as follows: (12) Based on the linearized models of each stage obtained above, a model can be established based on the rotor. dq The impedance model of the distributed synchronous condenser in the coordinate system is shown below.

[0030] (13) Transform the distributed synchronous condenser impedance model to a grid voltage-oriented model at the grid connection point. dq In the coordinate system, the transformation is performed in two steps. The first step is to transform to a synchronous rotation where the d-axis points to 0 degrees at time 0. dq Coordinate system (hereinafter referred to as common synchronization) dq (Coordinate system), and in this step consider the effect of small perturbations on the transformation angle. The transformation relationship is: (14) In the formula: It is a coordinate transformation matrix. It is the derivative term. It is adjusting the camera rotor. dq coordinate system d Axis and common synchronization dq coordinate system d angular difference of the axis This is its disturbance term.

[0031] in: (15) The generation is considered to be a disturbance of the rotor's electric angular velocity under disturbance, therefore: (16) Combining equations (9) and (13), we can obtain the common synchronization. dq Distributed phase condenser impedance in coordinate system: (17) The second step is to convert the impedance to grid voltage orientation. dq Coordinate system, because of public synchronization dq Coordinate system and grid voltage orientation dq Since the coordinate systems are all unperturbed, a direct transformation is sufficient: (18) In the formula matrix Angle output from phase-locked loop Calculated.

[0032] (2) Frequency domain transient overvoltage analysis model New energy multi-infeed system topology as follows Figure 3 As shown, the voltage-supported renewable energy power station feed-in node 1 to the distributed synchronous condenser includes... n ;node n +1 to n + m A passive node; node n + m +1 is connected to an infinite power grid. Now, a frequency domain transient overvoltage analysis model is established for this system.

[0033] To reflect the voltage information of the fault point in the model, this paper adopts the virtual node method: the fault point is treated as a node and included in the calculation of the node admittance matrix. Figure 3 In (a), it is assumed that the node n +1 represents the fault point; the wind farm during the fault period can be modeled as an equivalent current source. The distributed synchronous condenser impedance model was calculated in the previous section. Therefore, the distributed synchronous condenser can be regarded as an ideal voltage source and impedance. By connecting them in series, the equivalent circuit diagram of the new energy power station is obtained as follows: Figure 3 As shown in (c).

[0034] for Figure 3 For the new energy multi-infeed system shown in (a), the admittance matrix of some nodes in the AC power grid can be obtained as follows: The elements are: (19) In the formula It is the first Line number Column elements, It is a node Self-guided absorbance, It is a node With nodes The mutual admittance between them are all based on dq The line impedance matrix in the coordinate system is obtained, therefore Too matrix.

[0035] Equation (19) does not yet consider node 1 to n The admittance of the connected voltage support equipment is required, therefore, equation (19) needs to be modified to obtain the node admittance matrix. The elements to be corrected are: (20) In the formula Indicates the first The impedance of distributed synchronous condensers in new energy power stations at each node.

[0036] The relationship between the corrected nodal admittance matrix and voltage and current is as follows: (twenty one) In the formula ,in The first item is d shaft current, the second term is q shaft current; ,in Each node here dq Both current and voltage are based on the grid voltage orientation at this node. dq In a coordinate system.

[0037] The corrected node admittance matrix is ​​then divided into blocks, with nodes 1 through 1 receiving new energy feed-in. n With faulty nodes n +1 is considered an active node, and the remaining nodes are passive nodes. Matrix partitioning is performed accordingly. (twenty two) in, (twenty three) To analyze the entire process before and after the fault, the first step is to analyze the node. n A voltage drop occurred at point +1. When the system detected a voltage drop exceeding 0.1 pu at the grid connection point, the wind farm injected reactive current to support the grid connection point voltage. After a period of time, the fault was cleared, and the node... n When the voltage at point +1 rises and the grid connection point voltage is detected to be greater than 0.9 pu, the wind farm stops injecting reactive current into the grid connection point; therefore, the entire process can be considered as follows: According to Kron's reduction theorem, we can obtain: (twenty four) (24) will be expanded according to the new energy feed-in nodes and fault nodes: (25) In the formula , .

[0038] This yields the relationship between current and voltage at the new energy grid connection point and the fault node; however, when performing transient overvoltage analysis, what is known is the reactive current injected at the grid connection point and the magnitude of the voltage drop at the fault node, rather than the current at the grid connection point and the fault node on the right side of equation (25). Therefore, in order to make the analysis model fit the actual application, it is necessary to exchange... and Location: (26) in: (27) In equation (26), the node voltage and injected current of each node are used to establish the grid voltage orientation of that node. dq In coordinate system: Injected current at each node q The axis component corresponds to the reactive current injected into that node; the node voltage of each node... d The axis component corresponds to the voltage amplitude at that node.

[0039] Linearizing equation (26) yields the frequency domain transient overvoltage analysis model as follows: (28) In the formula , .

[0040] (3) Mapping relationship between frequency domain model and time domain transient overvoltage When a system fault occurs, without loss of generality, the reactive current injection process at the grid connection point and the voltage fluctuation at the fault node are abstracted as a step process. Given the magnitude of the reactive current injection and voltage fluctuation, the frequency domain fluctuation of the grid connection point voltage can be calculated using equation (28). Combining the inverse Laplace transform, the mapping relationship between the frequency domain transient overvoltage analysis model and the time domain transient overvoltage is as follows: (29) In the formula The output vector is the time-domain vector representing the incremental amplitude of the grid-connected point voltage / fault node current; complex frequency. ; The integration path was limited; It is the incremental vector of the current injected at the grid connection point / the voltage amplitude of the fault node, or simply the input vector.

[0041] The solution is based on the impedance of a distributed synchronous condenser. Typically, the impedance of the equipment is measured at discrete frequency points. Furthermore, the continuous inverse Laplace transform is difficult to solve directly in large-scale systems. Therefore, a more convenient and rapid solution method is needed. It is generally assumed that the impulse response of the power system under study is absolutely integrable, and choosing the imaginary axis as the integration path is feasible. ,at this time Simplified to Considering that temporary overvoltage fluctuations possess quasi-steady-state characteristics and are less affected by the system's high-frequency characteristics, the integration interval is limited to... Finally, by combining the discrete summation method, the discrete mapping relationship between the frequency domain transient overvoltage calculation model and the time domain transient overvoltage is obtained as follows: (30) In the formula The time series corresponding to the output vector; For the first Each sampling frequency, where the sampling step size is... .

[0042] (4) Calculation of transient overvoltage Given the reactive current injection process at the grid connection point before and after the fault, as well as the voltage fluctuation at the fault node, the voltage fluctuation at the grid connection point can be calculated. Assume the system... Stable operation before the specified time. A three-phase short-circuit fault occurred at node 2, causing the node voltage to drop. , When the wind farm injects reactive current into the grid connection point, the increase in reactive current is , The fault at point 2 was cleared, and the voltage rebounded. , When the wind farm stops reactive current injection.

[0043] Therefore, the entire process can be broken down into four events: ① Voltage drop at time node 2 ;② Reactive current injection at grid connection point at all times ;③ Voltage recovery at time node 2 ④ The wind farm stops reactive current at any time injection.

[0044] Assuming we want to obtain the grid connection point voltage from Time's up The voltage fluctuation curve 20ms after the fault. The voltage drop occurring at node 2 of the fault when simulating a system fault using an ideal voltage source. and voltage recovery Reactive injection current of grid connection All events are known; four events can yield four input vectors. , , , Combining equation (31), the corresponding output vector can be calculated as follows: , , , According to the principle of linear superposition, the output vectors of each event need to be time-shifted according to their occurrence time and superimposed within the observation time interval. Therefore, the voltage increment at the grid connection point during the entire fault process can be expressed as: (31) In the formula Time correspondence 20ms after the time point. Among them, (32) However, when performing transient overvoltage calculations on actual faulty systems, Voltage recovery at time node 2 The magnitude is unknown. Therefore, this paper proposes a method to predict the voltage recovery at fault nodes. The method for calculating the magnitude of transient overvoltage only requires... Voltage drop at time node 2 and Reactive current injection at grid connection point at all times This allows for the calculation of voltage fluctuation curves before and after a fault, especially after the fault is cleared.

[0045] Given events ①, ②, and ④, the output vector before fault clearance can be calculated using the method in equation (31): (33) At this point, the node of the previous sampling point before fault clearing can be obtained from the output vector. n +1 Injected current vector is During the failure, the node n +1 injection current is the fault-to-ground current. At the instant the fault is cleared, the fault to ground is disconnected, which can be considered as the injection current being instantaneously set to 0. This can be equivalent to a reverse step current disturbance. (Node) n The +1 current fluctuation is: (34) At the moment the fault is cleared, the wind farm at the grid connection point continues to inject reactive current due to the control lag effect. Combining equations (26) and (28), the magnitude of the frequency domain voltage rise at the instant of fault clearing can be obtained as follows: (35) By using equation (35) as the input variable for event ③, the output variable of event ③ can be calculated. Event ④ is the same as in the simulated fault, and the final output vector of the entire fault is obtained: (36) Therefore, by understanding the relationship between the injected current and voltage fluctuations at the fault point, it is possible to predict the voltage fluctuations throughout the entire fault process, especially the voltage recovery process after fault clearance, simply by knowing the magnitude of the injected current and the voltage drop caused by the fault. The peak transient overvoltage of the renewable energy grid connection point after fault clearance can be extracted as follows: (37) In the formula The new energy grid connection point before the fault occurred The steady-state voltage value; It is the output vector China New Energy Grid Connection Point of d Axis voltage components; It is the output vector China New Energy Grid Connection Point of q Axis voltage component.

[0046] (5) Verification by example The validity of this invention was verified using the PSCAD / EMTDC platform, and a system was built as follows: Figure 4 The diagram shows a new energy delivery system, with fault nodes configured and system settings included. The location of the fault is from The characteristic is that its nominal value corresponds to an inductance of 0.5H. At 15s, a three-phase short-circuit fault occurs on one of the two circuits of the outgoing line; the fault is a metallic fault (transition resistance). When the fault distance to the reactance fault is 10ms, the wind farm begins injecting reactive current into the grid connection point. The fault lasts for 200ms and is cleared in 15.2s. To verify the accuracy of the proposed transient overvoltage calculation method, the reactive current injection from the wind farm is stopped 30ms after the fault is cleared, causing the system to generate reactive power surplus and thus transient overvoltage.

[0047] To induce overvoltages of varying magnitudes in the system, the reactive current injected into the wind farm was artificially set to 0.4 pu, 0.6 pu, 0.8 pu, 1.0 pu, and 1.2 pu; the calculated voltage fluctuation curves are shown below. Figure 5 As shown.

[0048] like Figure 5 As shown, a comparison with the simulation curves reveals that the proposed transient overvoltage calculation method can calculate the grid connection point voltage fluctuation curve covering the entire fault process. Different reactive current injections result in different reactive surpluses, leading to different magnitudes of transient overvoltages. The calculated peak transient overvoltage has a very small error compared to the simulation value, verifying the correctness of the proposed method.

[0049] To verify the effectiveness of this invention in a new energy multi-infeed system, an IEEE 39-node system was built based on the PSCAD / EMTDC platform. Node 31 of the system is an infinite bus system, and nodes 34 to 39 are connected to new energy power stations containing distributed synchronous condensers. A metallic fault is simulated at node 19, such as... Figure 6 As shown.

[0050] The system was in steady state 60 seconds ago. A three-phase short-circuit fault occurred at node 19 60 seconds later. At 60.01 seconds, the renewable energy power station injected 1.2 pu of reactive current into the grid to support the grid voltage. The fault was cleared at 60.2 seconds, and the renewable energy power station stopped injecting reactive current at 60.23 seconds. The voltage fluctuation curves of the entire fault process at each renewable energy power station's grid connection point are shown below. Figure 7 As shown. By Figure 7 It is known that the calculated curve closely matches the simulated curve throughout the entire fault process, but there is a certain error, which is within an acceptable range. Therefore, this invention is not only applicable to transient overvoltage analysis of the sending-end system, but also applicable to new energy multi-infeed systems, where the dynamics of voltage support equipment can be considered in new energy power plants.

[0051] like Figure 8 As shown, another embodiment of the present invention provides a transient overvoltage quantification calculation system for a new energy multi-infeed system based on a wideband impedance model, comprising: Impedance Model Building Module: Used to build broadband impedance models for voltage-supported devices; Analysis model building module: used to build a frequency domain transient overvoltage analysis model that takes into account the dynamic characteristics of the system across the entire frequency band, based on the wideband impedance model; Mapping Relationship Establishment Module: Used to establish the mapping relationship between the frequency domain transient overvoltage analysis model and the time domain transient overvoltage; Voltage peak extraction module: It is used to calculate the voltage fluctuation curve of the new energy grid connection point during the entire fault process based on the mapping relationship, according to the reactive current injection process of the new energy grid connection point before and after the fault and the voltage fluctuation of the fault node, and extract the transient overvoltage peak from the voltage fluctuation curve.

[0052] A computer device is provided according to an embodiment of the present invention. This computer device includes a processor, a memory, and a computer program stored in the memory and executable on the processor. When the processor executes the computer program, it implements the steps in the various method embodiments described above. Alternatively, when the processor executes the computer program, it implements the functions of each module / unit in the various device embodiments described above.

[0053] The computer program can be divided into one or more modules / units, which are stored in the memory and executed by the processor to complete the present invention.

[0054] The computer device may be a desktop computer, laptop, handheld computer, or cloud server, etc. The computer device may include, but is not limited to, a processor and memory.

[0055] The processor may be a central processing unit (CPU), or other general-purpose processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc.

[0056] The memory can be used to store the computer program and / or module, and the processor implements various functions of the computer device by running or executing the computer program and / or module stored in the memory, and by calling the data stored in the memory.

[0057] If the modules / units integrated into the computer device are implemented as software functional units and sold or used as independent products, they can be stored in a computer-readable storage medium. Based on this understanding, all or part of the processes in the methods of the above embodiments can also be implemented by a computer program instructing related hardware. The computer program can be stored in a computer-readable storage medium, and when executed by a processor, it can implement the steps of the various method embodiments described above. The computer program includes computer program code, which can be in the form of source code, object code, executable files, or certain intermediate forms. The computer-readable medium can include: any entity or device capable of carrying the computer program code, recording media, USB flash drives, portable hard drives, magnetic disks, optical disks, computer memory, read-only memory, random access memory, electrical carrier signals, telecommunication signals, and software distribution media, etc. It should be noted that the content included in the computer-readable medium can be appropriately added or removed according to the requirements of legislation and patent practice in the jurisdiction. For example, in some jurisdictions, according to legislation and patent practice, computer-readable media do not include electrical carrier signals and telecommunication signals.

[0058] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. It will be apparent to those skilled in the art that the invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered illustrative and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the scope of the invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0059] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can be appropriately combined to form other embodiments that can be understood by those skilled in the art. The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made based on the technical concept proposed in this invention shall fall within the scope of protection of the claims of this invention.

Claims

1. A method for quantifying and calculating transient overvoltages throughout the entire process of a new energy multi-infeed system based on a wideband impedance model, characterized in that, Includes the following steps: Establish a broadband impedance model for voltage-supported equipment; Based on the aforementioned wideband impedance model, a frequency domain transient overvoltage analysis model considering the dynamic characteristics of the system across the entire frequency band is established. Establish the mapping relationship between the frequency domain transient overvoltage analysis model and the time domain transient overvoltage; Based on the reactive current injection process of the new energy grid connection point before and after the fault and the voltage fluctuation of the fault node, the voltage fluctuation curve of the new energy grid connection point during the entire fault process is calculated based on the mapping relationship, and the transient overvoltage peak value is extracted from the voltage fluctuation curve.

2. The method for quantifying and calculating transient overvoltage throughout the entire process of a new energy multi-infeed system based on a wideband impedance model, as described in claim 1, is characterized in that... The voltage support device is a distributed synchronous condenser; The establishment of the broadband impedance model for the voltage support device includes: Linearization and Laplace transform of the voltage and flux linkage equations of the distributed synchronous condenser body are performed to obtain the small-signal voltage-current relationship. Combining the rotor motion equation and the electromagnetic torque equation, where the mechanical torque input is zero, the flux disturbance term is derived from the voltage equation and the flux equation. By combining the small-signal voltage-current relationship, the rotor motion equation, and the electromagnetic torque equation, and eliminating intermediate variables, the impedance model of the distributed synchronous condenser in the rotor dq coordinate system is obtained.

3. The method for quantifying and calculating transient overvoltage throughout the entire process of a new energy multi-infeed system based on a wideband impedance model, as described in claim 2, is characterized in that... Establishing a broadband impedance model for voltage-supported equipment also includes: The impedance model in the rotor dq coordinate system is transformed to the common synchronous dq coordinate system. The influence of small disturbances on the transformation angle is considered during the transformation. Then, the impedance in the common synchronous dq coordinate system is transformed to the grid voltage-oriented dq coordinate system to obtain the broadband impedance model of the distributed synchronous condenser.

4. The method for quantifying and calculating transient overvoltage throughout the entire process of a new energy multi-infeed system based on a wideband impedance model, as described in claim 1, is characterized in that... The establishment of a frequency domain transient overvoltage analysis model includes: The fault point is treated as a virtual node and included in the node admittance matrix calculation to form a partial node admittance matrix of the AC power grid. The node admittance matrix is ​​corrected based on the impedance of the voltage support equipment connected to each node; The corrected node admittance matrix is ​​divided into blocks according to the new energy feed-in nodes, fault nodes and passive nodes. After Kron reduction simplification, the current and voltage relationship of the new energy grid connection point and the fault node is obtained. By swapping the positions of the input and output variables in the current-voltage relationship and performing linearization, a frequency domain transient overvoltage analysis model is obtained.

5. The method for quantifying and calculating transient overvoltage throughout the entire process of a new energy multi-infeed system based on a wideband impedance model, as described in claim 1, is characterized in that... Establishing the mapping relationship between the frequency domain transient overvoltage analysis model and the time domain transient overvoltage includes: The reactive current injection process at the grid connection point and the voltage fluctuation at the fault node are abstracted as a step process, and the frequency domain fluctuation of the grid connection point voltage is calculated in combination with the frequency domain transient overvoltage analysis model. The mapping relationship between the frequency domain transient overvoltage analysis model and the time domain transient overvoltage is established by combining the inverse Laplace transform; When performing the inverse Laplace transform on the frequency domain fluctuation, the imaginary axis is selected as the integration path, and the mapping relationship between the frequency domain model and the time domain transient overvoltage is obtained by combining the discrete summation method.

6. The method for quantifying and calculating transient overvoltage throughout the entire process of a new energy multi-infeed system based on a wideband impedance model, as described in claim 1, is characterized in that... The voltage fluctuation curve of the new energy grid connection point during the entire fault process includes: The entire fault process is decomposed into multiple events, which include at least the voltage drop at the fault node, reactive current injection at the grid connection point, voltage recovery at the fault node, and cessation of reactive current injection. The magnitude of the voltage recovery at the fault node is determined as follows: the voltage recovery at the moment of fault clearance is calculated by combining the fault node injected current vector of the previous sampling point before fault clearance with the boundary condition that the node injected current is set to zero at the moment of fault clearance, and used as the input variable for the fault node voltage recovery event. Based on the occurrence time of each event, the output vector corresponding to each event is calculated according to the mapping relationship, and the voltage increment of the grid connection point during the entire fault process is obtained according to the principle of time shift and linear superposition. Extract the transient overvoltage peak from the d-axis and q-axis components of the voltage fluctuation at the grid connection point after fault clearance.

7. A system for quantifying and calculating transient overvoltages throughout the entire process of a new energy multi-infeed system based on a wideband impedance model, used to implement the method for quantifying and calculating transient overvoltages throughout the entire process of a new energy multi-infeed system based on a wideband impedance model as described in any one of claims 1-6, comprising: Impedance Model Building Module: Used to build broadband impedance models for voltage-supported devices; Analysis model building module: used to build a frequency domain transient overvoltage analysis model that takes into account the dynamic characteristics of the system across the entire frequency band, based on the wideband impedance model; Mapping Relationship Establishment Module: Used to establish the mapping relationship between the frequency domain transient overvoltage analysis model and the time domain transient overvoltage; Voltage peak extraction module: It is used to calculate the voltage fluctuation curve of the new energy grid connection point during the entire fault process based on the mapping relationship, according to the reactive current injection process of the new energy grid connection point before and after the fault and the voltage fluctuation of the fault node, and extract the transient overvoltage peak from the voltage fluctuation curve.

8. A computer device, comprising a memory, a processor, and a computer program stored in the memory, characterized in that, The processor executes the computer program to implement the steps of the method for quantifying and calculating transient overvoltages throughout the entire process of a new energy multi-infeed system based on a wideband impedance model, as described in any one of claims 1-6.

9. A computer-readable storage medium having a computer program stored thereon, characterized in that, When executed by a processor, the computer program implements the steps of the method for quantifying and calculating transient overvoltages throughout the entire process of a new energy multi-infeed system based on a wideband impedance model, as described in any one of claims 1-6.

10. A computer program product, comprising a computer program, characterized in that, When executed by a processor, the computer program implements the steps of the method for quantifying and calculating transient overvoltages throughout the entire process of a new energy multi-infeed system based on a wideband impedance model, as described in any one of claims 1-6.

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