Voltage phase jump prediction method and system for asynchronous interconnection system receiving end power grid

Abstract

The invention discloses a voltage phase jump prediction method and system for a receiving-end power grid of an asynchronous interconnection system, and relates to the technical field of electric power engineering.The method comprises the steps that a network equation is established based on composition structures, distribution characteristics and transient characteristics of receiving-end power grid elements of the asynchronous interconnection system; electrical behaviors of the commutation bus phase of the asynchronous interconnection system under different fault conditions are accurately reflected, and a single-feed-in AC / DC system equivalent model before and after a fault is obtained according to a network equation of a receiving end power grid of the asynchronous interconnection system; solving the equivalent power supply voltage and impedance of the receiving-end power grid before and after the fault and the mutual impedance change between nodes after the fault, and finally calculating the phase jump of the current conversion bus voltage of the receiving-end power grid according to the phase relation of the single-feed-in AC / DC system equivalent model before and after the fault. The problem that in the prior art, a quantization method for phase jump is not accurate enough or dynamic characteristics of phase change cannot be reflected is solved, and a powerful basis is provided for fault analysis, state monitoring and dynamic scheduling of a system.

Description

Technical Field

[0001] The present invention relates to the technical field of electric power engineering, and more particularly to a method and system for predicting voltage phase jumps in a receiving-end power grid of an asynchronous interconnected system. Background Art

[0002] At present, with the rapid development of social economy, the demand for large-capacity and long-distance power transmission is increasing day by day, which has promoted the widespread application of conventional direct current transmission systems (LCC-HVDC) around the world. In some areas, 19 ultra-high voltage direct current transmission projects have been built for east-west power transmission, with a total transmission capacity of more than 270 million kW. The power grid is gradually changing from a large synchronous grid to an asynchronous interconnected grid. At the same time, the proportion of new energy generators in the power grid is increasing. LCC-HVDC and new energy generators use power electronic devices as key technologies, and power electronic devices have fast shutdown and nonlinear characteristics, which makes the power system present more complex and serious fault phenomena and risks when a fault occurs.

[0003] Phase jump is another important feature of voltage drop besides residual voltage and fault time. Research has found that the phase jump angle will affect the synchronization between the grid-following inverter and the grid, cause distributed photovoltaic power reduction and machine switching, and stimulate double-fed wind turbine rotor overcurrent, thus threatening the fault ride-through capability of new energy power stations and the stable operation of the power system. However, phase jump is still an understudied object, and its jump amplitude has not been studied so far, and its quantification needs further research.

[0004] Therefore, how to accurately quantify the voltage phase jump of the receiving-end power grid of the asynchronous interconnected system is a problem that technical personnel in this field need to solve urgently. Summary of the invention

[0005] In view of this, the present invention provides a method and system for predicting voltage phase jump of a receiving-end power grid of an asynchronous interconnected system, so as to solve the problems existing in the background technology.

[0006] In order to achieve the above object, the present invention adopts the following technical solution:

[0007] A voltage phase jump prediction method for a receiving-end power grid of an asynchronous interconnected system, comprising:

[0008] Based on three-phase symmetrical fault, the network equation of the receiving-end power grid of the asynchronous interconnected system is established;

[0009] According to the network equation of the receiving-end power grid of the asynchronous interconnected system, the equivalent model of the single-infeed AC / DC system before and after the fault is obtained;

[0010] Based on the equivalent model of the single-feed AC / DC system before the fault, the equivalent power supply voltage and impedance of the receiving-end power grid are solved;

[0011] Calculate the change in mutual impedance between nodes after a fault occurs;

[0012] Based on the equivalent model of the single-infeed AC / DC system after the fault, the equivalent power supply voltage and impedance of the receiving-end power grid are solved;

[0013] Based on the equivalent power supply voltage and impedance of the receiving power grid before and after the fault and the change of mutual impedance between nodes after the fault occurs, the phase jump of the receiving power grid commutation bus voltage is calculated according to the phase relationship of the equivalent model of the single-feed AC / DC system before and after the fault.

[0014] Optionally, the network equation of the receiving-end power grid of the asynchronous interconnected system is specifically:

[0015]

[0016] In the formula, They represent the node voltage, the current flowing into the node and the elements in the node impedance matrix respectively; the subscripts CZ, CI, LCC, f and E represent the corresponding node types, namely constant impedance load, constant current load, DC feed-in node, fault node and generator node, where the bold symbols represent matrices or vectors, and the non-bold symbols represent single elements.

[0017] Optionally, the equivalent model of the single-feed AC / DC system before and after the fault is obtained according to the network equation of the receiving-end power grid of the asynchronous interconnected system:

[0018] The network equation of the receiving-end power grid of the asynchronous interconnected system is subjected to matrix calculation to obtain the following equation:

[0019]

[0020] Combining the two equations in the above formula, we can get the expression of the equivalent model of the single-feed AC / DC system:

[0021]

[0022] According to the expression of the equivalent model of the single-infeed AC / DC system, the equivalent model of the single-infeed AC / DC system before and after the fault is obtained.

[0023] Optionally, the formula for calculating the change in mutual impedance between nodes after a fault occurs is:

[0024]

[0025] In the formula, Z i ' ,j is the mutual impedance between nodes i and j after the change, Z i,j is the impedance between node i and node j before the fault, Z i,fis the impedance between node i and node f, Z f,j is the impedance between node j and node f, Z f,f is the self-impedance of node f, R f is the resistance of the node.

[0026] Optionally, based on the equivalent model of the single-feed AC / DC system after the fault, the expression for solving the equivalent power supply voltage and impedance of the receiving-end power grid is:

[0027]

[0028] In the formula, is the commutation bus voltage after the fault, is the equivalent voltage source of the AC system after the fault, is the equivalent impedance of the AC system after the fault, is the current flowing from LCC-HVDC to the AC system after the fault, is the impedance between nodes after the fault, and the subscripts CZ, CI, LCC, f, and E represent the corresponding node types, i.e., constant impedance load, constant current load, DC feed-in node, fault node, and generator node. The bold symbols represent matrices or vectors, and the non-bold symbols represent single elements.

[0029] Optionally, the formula for calculating the phase jump of the commutation bus voltage of the receiving-end power grid is:

[0030] Δθ=θ L ' CC -θ LCC =(θ L ' CC -θ e ' q +θ e ' q )-(θ LCC -θ eq +θ eq );

[0031] Where Δθ is the phase jump, θ L ' CC ,θ LCC is the voltage phase of the commutation bus, θ e ' q ,θ eq It is the voltage phase of the equivalent voltage source in the AC system.

[0032] Optionally, the method further includes solving a formula for phase jump of the commutation bus voltage of the receiving-end power grid, specifically:

[0033] θ L ' LCC -θ e 'q ≈0;

[0034]

[0035] In the formula, It is the current injected by LCC-HVDC into the receiving grid before the fault.

[0036] A voltage phase jump prediction system for a receiving-end power grid of an asynchronous interconnected system, comprising:

[0037] The network equation building module builds the network equation of the receiving-end power grid of the asynchronous interconnected system based on three-phase symmetrical faults;

[0038] The equivalent model building module obtains the equivalent model of the single-feed AC / DC system before and after the fault according to the network equation of the receiving-end power grid of the asynchronous interconnected system;

[0039] The equivalent data calculation module solves the equivalent power supply voltage and impedance of the receiving-end power grid based on the equivalent model of the single-feed AC / DC system before the fault;

[0040] Calculate the change in mutual impedance between nodes after a fault occurs;

[0041] Based on the equivalent model of the single-infeed AC / DC system after the fault, the equivalent power supply voltage and impedance of the receiving-end power grid are solved;

[0042] The phase jump result output module calculates the phase jump of the receiving-end power grid commutation bus voltage based on the phase relationship of the equivalent model of the single-feed AC / DC system before and after the fault, based on the equivalent power supply voltage and impedance of the receiving-end power grid before and after the fault and the change in mutual impedance between nodes after the fault occurs.

[0043] It can be seen from the above technical scheme that, compared with the prior art, the present invention discloses a method and system for predicting voltage phase jumps in a receiving-end power grid of an asynchronous interconnected system, establishes a network equation based on the composition structure, distribution characteristics and transient characteristics of the receiving-end power grid elements of the asynchronous interconnected system, accurately reflects the electrical behavior of the commutation bus phase of the asynchronous interconnected system under different fault conditions, and proposes a quantitative analysis method for phase jumps, which solves the problem that the quantification method of phase jumps in the prior art is not accurate enough or cannot reflect the dynamic characteristics of phase changes, and provides a strong basis for system fault analysis, status monitoring and dynamic scheduling. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0045] Figure 1 A schematic diagram of the receiving-end power grid structure of the asynchronous interconnection system provided by the present invention;

[0046] Figure 2 A schematic diagram of the structure of an equivalent model of a single-feed AC / DC system provided by the present invention;

[0047] in, Figure 2 (a) is the equivalent model of a single-infeed AC / DC system before the fault. Figure 2 (b) is the equivalent model of the single-infeed AC / DC system before the fault;

[0048] Figure 3 A schematic diagram of a short-circuit loop formed on the DC side of an inverter station after FCF occurs provided by the present invention;

[0049] Figure 4 The phasor diagram of each variable in formula (9) provided by the present invention;

[0050] Figure 5 Provide an existing phase jump analysis method for the present invention;

[0051] Figure 6 The IEEE39 node system provided by the present invention is used as a receiving-end power grid;

[0052] Figure 7 A schematic diagram of an LCC-HVDC system for asynchronous interconnection provided by the present invention;

[0053] in Figure 7 (a) is the LCC-HVDC system of model 1, Figure 7 (b) LCC-HVDC system of model 2;

[0054] Figure 8 The calculation results of each example provided by the present invention; wherein Figure 8 (a) Figure 8 (b) Figure 8 (c) shows the calculation results of Case 1, Case 2, and Case 3 respectively;

[0055] Fig. 9 A flow chart for calculating a voltage phase jump value provided by the present invention. DETAILED DESCRIPTION

[0056] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. 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.

[0057] The embodiment of the present invention discloses a method for predicting voltage phase jump of a receiving-end power grid of an asynchronous interconnected system, comprising:

[0058] Based on three-phase symmetrical fault, the network equation of the receiving-end power grid of the asynchronous interconnected system is established;

[0059] According to the network equation of the receiving-end power grid of the asynchronous interconnected system, the equivalent model of the single-infeed AC / DC system before and after the fault is obtained;

[0060] Based on the equivalent model of the single-feed AC / DC system before the fault, the equivalent power supply voltage and impedance of the receiving-end power grid are solved;

[0061] Calculate the change in mutual impedance between nodes after a fault occurs;

[0062] Based on the equivalent model of the single-infeed AC / DC system after the fault, the equivalent power supply voltage and impedance of the receiving-end power grid are solved;

[0063] Based on the equivalent power supply voltage and impedance of the receiving power grid before and after the fault and the change of mutual impedance between nodes after the fault occurs, the phase jump of the receiving power grid commutation bus voltage is calculated according to the phase relationship of the equivalent model of the single-feed AC / DC system before and after the fault.

[0064] In a specific embodiment, the model of the receiving-end power grid of the asynchronous interconnected system is established:

[0065] An asynchronous interconnected system refers to two or more regional power grids that are interconnected through high-voltage direct current transmission technology. Due to the decoupling characteristics of direct current transmission, the interconnected power grids can operate at different frequencies. Conventional direct current transmission system (LCC-HVDC) is the most common high-voltage direct current transmission technology used in asynchronous interconnected systems.

[0066] The receiving end system of LCC-HVDC can be Figure 1 To represent the dynamic characteristics of the AC-DC system during an AC fault, the system can use generators (G1, G2, ..., G n ), constant impedance load (CZ1, CZ2, ..., CZ n ) and constant current load (CI1,CI2,...,CI n ) and other components. Figure 1In the receiving grid, LCC-HVDC is fed into the DC feed-in node, and the fault in the network occurs at the fault node R f .

[0067] The voltage sources corresponding to the generator are represented by E1, E2, ..., E n According to the constant flux model of synchronous machines, the amplitude and phase of these voltage sources are considered constant before and during the fault.

[0068] A constant impedance load is equivalent to a constant impedance and can be further considered as part of the passive network, so it does not need to be specifically represented in the network equation. A constant current load can be considered as a current source flowing out of the passive network, and its corresponding current is marked as I LD1 ,I LD2 ,...,I LDn The LCC-HVDC is connected to the receiving grid at the feeding node, and an AC fault occurs at the fault node f.

[0069] In the specific analysis, the mutual coupling between the three-phase voltages makes it difficult to change the voltage phase of an asymmetric fault. However, a symmetric fault will cause a phase jump in the voltage of all phases, so it poses the greatest threat to the DC system. Therefore, the model is established based on a three-phase symmetric fault. From this, we can get Figure 1 The network equation of the receiving-end power grid of the asynchronous interconnected system is shown in equation (1).

[0070]

[0071] In the network equation shown in equation (1), it is assumed that no current is injected into node f before the AC fault occurs.

[0072] In the formula, They represent the node voltage, the current flowing into the node and the elements in the node impedance matrix respectively; the subscripts CZ, CI, LCC, f and E represent the corresponding node types, namely constant impedance load, constant current load, DC feed-in node, fault node and generator node, where the bold symbols represent matrices or vectors, and the non-bold symbols represent single elements.

[0073] In a specific embodiment, the equivalent model of a single-infeed AC / DC system is established:

[0074] Based on the network equation of the receiving-end power grid of the asynchronous interconnected system shown in equation (1), equation (2) can be obtained through matrix calculation.

[0075]

[0076] Combining the two equations in (2), we can get equation (3). Equation (3) means Figure 2(a) shows the equivalent model of a single-infeed AC / DC system, where U LCC is the AC voltage at the receiving-end power grid commutation bus, E eq It is the equivalent power supply voltage of the receiving power grid. eq and X eq is the resistance and reactance of the equivalent system, and θ LCC and θ eq Respectively represent U LCC and E eq phase.

[0077]

[0078] After an AC fault occurs, the LCC-HVDC system will experience a first commutation failure (FCF). Figure 2 The DC side of the DC converter station shown in (a) will experience a short circuit, resulting in an interruption of active power transmission, that is, the DC active power P d = 0, after FCF occurs, the short-circuit circuit diagram formed on the DC side of the inverter station is as follows Figure 3 Therefore, the reactive power absorbed by the inverter is Q d is also zero, as shown in formula (4), where It indicates the power factor angle flowing into the converter valve. This is equivalent to the converter valve of the inverter being disconnected from the receiving grid, and the converter station no longer absorbs the reactive power emitted by the reactive compensation device. The reactive compensation CLCC is directly connected to the AC system, and no reactive power flows into the converter. Figure 2 (b) as shown.

[0079]

[0080] The occurrence of a fault is equivalent to the node f passing through the resistor R f Grounding causes the elements of the node impedance matrix to change. For nodes i and j in the passive network, the mutual impedance between them changes as shown in formula (5) due to the grounding of node f. Similarly, the process of connecting CLCC to the AC system can also be modified according to formula (5).

[0081]

[0082] In the formula, Z i ' ,j is the mutual impedance between nodes i and j after the change, Z i,j is the impedance between node i and node j before the fault, Z i,f is the impedance between node i and node f, Z f,j is the impedance between node j and node f, Z f,f is the self-impedance of node f, R f is the resistance of the node.

[0083] Therefore, during a fault, equation (3) becomes (6), where the prime sign on the matrix indicates a new matrix that is calculated after considering the fault R f and C LCC formed after the changes.

[0084]

[0085] In the formula, is the commutation bus voltage after the fault, is the equivalent voltage source of the AC system after the fault, is the equivalent impedance of the AC system after the fault, is the current flowing from LCC-HVDC to the AC system after the fault, is the impedance between nodes after the fault, and the subscripts CZ, CI, LCC, f, and E represent the corresponding node types, i.e., constant impedance load, constant current load, DC feed-in node, fault node, and generator node. The bold symbols represent matrices or vectors, and the non-bold symbols represent single elements.

[0086] Therefore, the interaction between the inverter station and the receiving grid is simplified to an equivalent circuit based on equations (3) and (6), as follows: Figure 2 As shown, Figure 2 (a) is the equivalent model of a single-infeed AC / DC system before the fault. Figure 2 (b) is the equivalent model of the single-infeed AC / DC system before the fault; Figure 2 It shows how the occurrence of an AC fault changes the equivalent model of the receiving grid and causes the equivalent voltage source E of the AC system to eq and impedance Z eq changes have occurred.

[0087] In a specific embodiment, the calculation method of the commutation bus voltage phase jump is specifically as follows:

[0088] based on Figure 2 The equivalent model of the single-infeed AC / DC system shown in the figure can be used Figure 2 The phase relationship of the equivalent system is used to calculate the phase jump of the receiving-end power grid commutation bus voltage, as shown in equation (7).

[0089] Δθ=θ L ' CC -θ LCC =(θ L ' CC -θ e ' q +θ e ' q )-(θ LCC -θ eq +θ eq) (7)

[0090] Where Δθ is the phase jump, θ L ' CC ,θ LCC is the voltage phase of the commutation bus, θ e ' q ,θ eq It is the voltage phase of the equivalent voltage source in the AC system.

[0091] After the fault, the DC active power P d When U' becomes 0, the DC current ILCC flowing from the DC system to the receiving grid will also drop to 0. LCC will be close to the equivalent voltage source E' eq , and result in similar phase values, as shown in equation (8). Equation (7) can be further expressed as equation (9), which shows how to calculate the phase jump Δθ of the voltage.

[0092] θ L ' CC -θ e ' q ≈0(8)

[0093]

[0094] In the formula, It is the current injected by LCC-HVDC into the receiving grid before the fault.

[0095] According to equation (9), the phase jump Δθ consists of two main parts in the formula, denoted as sub-term (1) and sub-term (2).

[0096] Sub-item (1) represents the phase difference between the equivalent voltage sources before and during the fault. This phase change is caused by the change of the elements of the network node impedance matrix, as shown in equation (5). Therefore, sub-item (1) originates from the transient change of the network structure caused by the fault.

[0097] Sub-item (2) represents the voltage of the receiving-end commutation bus before the fault and the equivalent voltage source E eq The phase difference between the voltages. Therefore, sub-item (2) originates from the transient change of the DC power flow caused by the fault. Although the fault in the sending grid does not affect the network structure of the receiving grid, it still causes a phase jump in the receiving grid converter bus by changing the DC power flow. Therefore, the conclusion drawn from equation (9) is also applicable to the fault in the sending grid, but in this case, only sub-item (2) needs to be considered.

[0098] In practical applications, grid operators can obtain data on generators, loads, DC systems, and faults, and use equations (3), (6), and (9) to calculate the phase jump of the receiving grid commutation bus voltage. By considering network characteristics and modeling LCC-HVDC based on its power characteristics, the proposed single-feed AC / DC system equivalent model is applicable to different power systems with LCC-HVDC asynchronous interconnection and different fault locations, effectively overcoming the limitations and errors of existing models in calculating voltage phase jumps.

[0099] Figure 4 shows the phasor diagram of the variables in equation (9) and also illustrates that θ eq ,θ' eq ,θ LCC The relationship between and PAJ.

[0100] In a specific embodiment, the following comparative analysis is introduced:

[0101] (1) Comparison with existing voltage phase jump analysis methods

[0102] Figure 5 The calculation model shown is a widely used voltage phase jump analysis model. However, this model is only applicable to radial distribution networks and is not applicable to transmission systems with network structures. In addition, this method ignores the load current, which has a large proportion in the actual power system. This method also has the significant disadvantage of low calculation accuracy.

[0103] (2) Correctness of the proposed voltage phase jump analysis method

[0104] 1. Introduction to the verification model

[0105] Figure 6 The IEEE 39-bus system shown is used as the receiving-end grid. In order to incorporate constant current loads for verification, the loads of 7 nodes in the original system are replaced with constant current loads, accounting for 44.72% of the total system load. Other parameters such as transmission lines, load levels, generator parameters, and transformer parameters are consistent with the standard IEEE 39-bus system.

[0106] The LCC-HVDC system that realizes asynchronous interconnection of systems is as follows: Figure 7 ,in Figure 7 (a) is the LCC-HVDC system of model 1, Figure 7 (b) is the LCC-HVDC system of model 2. The LCC-HVDC system is based on the CIGRE LCC-HVDC benchmark system. The equivalent Thevenin system is replaced by a transmission line with an impedance of 0.0529+j0.529 (Ω / km) in this model, and the other system parameters are the same as the original system.

[0107] Model 1 and Model 2 are introduced as follows:

[0108] Model 1: LCC-HVDC feed-in at point 1 Figure 6 The receiving-end grid shown, in which the inverter station is connected to node 38, and the transformer between nodes 29 and 38 is replaced by a 10-kilometer transmission line.

[0109] Model 2: LCC-HVDC feed-in at point 2 Figure 6 The receiving grid shown, where the inverter station is connected to node 30, and the transformer between nodes 02 and 30 is replaced by a 10 km transmission line. In order to balance the active power brought by the DC system, the generator G8 and its corresponding transformer are removed.

[0110] 2. Correctness verification

[0111] Assume that the voltage phase angle calculated in this embodiment jumps to Δθ cal , the measured value is Δθ mea The following three cases based on Model 1 and Model 2 are used for verification. The calculated voltage phase angle jump values ​​are obtained by running a custom script in Windows 11 system, 3.70GHz main frequency, 16GB memory and MATLAB R2022b environment, while the measured values ​​are from the corresponding simulation in PSCAD. Due to the high accuracy of PSCAD simulation, Δθ mea Can be used as Δθ cal Effective verification of accuracy.

[0112] Case 1: Set a three-phase fault at the receiving end at the odd nodes and node 38 (DC feed-in node) of model 1, R f =0.1Ω.

[0113] Case 2: A three-phase fault is set at the receiving end at the even nodes and node 30 (DC feed-in node) of model 2, and Rf = 0.1Ω.

[0114] Case 3: Set a three-phase fault at the receiving end at node 26 of model 1, R f The range is 1 to 20Ω.

[0115] The calculation results of each example are as follows Figure 8 As shown, Figure 8 (a) Figure 8 (b) Figure 8 (c) shows the calculation results of Case 1, Case 2, and Case 3 respectively.

[0116] according to Figure 8(a), the error range of each node in Case 1 is -4.324° to 3.552°, and the maximum absolute error occurs at node 29. Due to the failure of node 29, Δθ cal =-96.713°, Δθ mea =-101.037°, and the relative error is 4.230%. This relative error is very small and falls within an acceptable range, and is acceptable when predicting the effect of phase jump on CFFR.

[0117] according to Figure 8 (b), the error range of each node in Case 2 is from -1.987° to 0.892°, and the maximum absolute error occurs at node 34. Correspondingly, the relative error is 11.352%. This is the largest relative error among all the data, indicating that other data points do not reach such a high error level.

[0118] according to Figure 8 (c) With R f The increase of θ PAJ In case 3, different R f The error range is 0.380° to 3.725°, with the maximum absolute error occurring at R f =12Ω. When node 29 is connected to R f When a fault occurs, the corresponding Δθ cal =-75.046°, Δθ mea =-71.321°, and the relative error is 5.223%, both within the acceptable range. It is worth noting that according to relevant literature, the fault resistance of the high-voltage transmission network is all within the range of 0-10Ω. Therefore, R is used in Case 3. f =1-20Ω fully represents the actual conditions.

[0119] Table 1 shows the statistical results of cases 1 to 3. According to Table 1, Δθ in cases 1 to 3 cal RMS value and Δθ mea The RMS values ​​of the sensors are very close, with differences of 0.941°, 0.527°, and -1.930°, respectively. In addition, the RMS relative errors are 6.232%, 7.394%, and 2.836%, respectively, all within the acceptable range.

[0120] Table 1 Δθ of Examples 1 to 2 cal and Δθ mea Statistical analysis

[0121]

[0122] It is worth noting that the significant negative impact of voltage phase jumps on DC systems is only apparent when the magnitude is large. Therefore, an error of a few degrees has limited impact on prediction and analysis. Therefore, it can be concluded that the proposed method is able to accurately calculate voltage phase jumps and is suitable for various applications such as power system planning, control system design, and grid protection.

[0123] This embodiment aims to obtain the AC voltage phase jump value of the commutation bus of the asynchronous interconnected receiving-end power grid by using the network structure. Since a large number of measurement and detection equipment are configured in modern power systems, information such as the network topology and load components can be easily obtained, thereby predicting the voltage phase jump. The specific example is as follows:

[0124] Will Figure 6 and Figure 7 Taking the model 3 shown in the figure as an example, first input the network topology, CZ load and other relevant data of the model 3 into the program. Then, these data are sequentially formed into the network impedance matrices Z and Z' before and after the fault through a custom script, and the voltage phase jump when the fault occurs at the fault node f is calculated using formulas (3), (5), (6) and (9). By repeating this process for different fault nodes, the voltage phase jump under various fault conditions in model 3 is obtained. The calculated value of the voltage phase jump is obtained by running the custom script under WIN11, 3.70GHz main frequency, 16GB memory and MATLAB R2022b environment. The calculation logic of the method (custom script) adopted in this embodiment is as follows Fig. 9 shown.

[0125] A voltage phase jump prediction system for a receiving-end power grid of an asynchronous interconnected system, comprising:

[0126] The network equation building module builds the network equation of the receiving-end power grid of the asynchronous interconnected system based on three-phase symmetrical faults;

[0127] The equivalent model building module obtains the equivalent model of the single-feed AC / DC system before and after the fault according to the network equation of the receiving-end power grid of the asynchronous interconnected system;

[0128] The equivalent data calculation module solves the equivalent power supply voltage and impedance of the receiving-end power grid based on the equivalent model of the single-feed AC / DC system before the fault;

[0129] Calculate the change in mutual impedance between nodes after a fault occurs;

[0130] Based on the equivalent model of the single-infeed AC / DC system after the fault, the equivalent power supply voltage and impedance of the receiving-end power grid are solved;

[0131] The phase jump result output module calculates the phase jump of the receiving-end power grid commutation bus voltage based on the phase relationship of the equivalent model of the single-feed AC / DC system before and after the fault, based on the equivalent power supply voltage and impedance of the receiving-end power grid before and after the fault and the change in mutual impedance between nodes after the fault occurs.

[0132] In this specification, each embodiment is described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the embodiments can be referred to each other. For the device disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is relatively simple, and the relevant parts can be referred to the method part.

[0133] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for predicting voltage phase jump of a receiving-end power grid of an asynchronous interconnected system, characterized in that: include: Based on three-phase symmetrical fault, the network equation of the receiving-end power grid of the asynchronous interconnected system is established; According to the network equation of the receiving-end power grid of the asynchronous interconnected system, the equivalent model of the single-infeed AC / DC system before and after the fault is obtained; Based on the equivalent model of the single-feed AC / DC system before the fault, the equivalent power supply voltage and impedance of the receiving-end power grid are solved; Calculate the change in mutual impedance between nodes after a fault occurs; Based on the equivalent model of the single-infeed AC / DC system after the fault, the equivalent power supply voltage and impedance of the receiving-end power grid are solved; Based on the equivalent power supply voltage and impedance of the receiving power grid before and after the fault and the change of mutual impedance between nodes after the fault occurs, the phase jump of the commutation bus voltage of the receiving power grid is calculated according to the phase relationship of the equivalent model of the single-feed AC / DC system before and after the fault.

2. A method for predicting voltage phase jump of a receiving-end power grid of an asynchronous interconnected system according to claim 1, characterized in that: The network equation of the receiving-end power grid of the asynchronous interconnected system is specifically: In the formula, They represent the node voltage, the current flowing into the node and the elements in the node impedance matrix respectively; the subscripts CZ, CI, LCC, f and E represent the corresponding node types, namely constant impedance load, constant current load, DC feed-in node, fault node and generator node, where the bold symbols represent matrices or vectors, and the non-bold symbols represent single elements.

3. The voltage phase jump prediction method for the receiving-end power grid of an asynchronous interconnected system according to claim 2 is characterized in that: According to the network equation of the receiving-end power grid of the asynchronous interconnected system, the equivalent model of the single-feed AC / DC system before and after the fault is obtained as follows: The network equation of the receiving-end power grid of the asynchronous interconnected system is subjected to matrix calculation to obtain the following equation: Combining the two equations in the above formula, we can get the expression of the equivalent model of the single-feed AC / DC system: According to the expression of the equivalent model of the single-infeed AC / DC system, the equivalent model of the single-infeed AC / DC system before and after the fault is obtained.

4. The method for predicting voltage phase jump of a receiving-end power grid of an asynchronous interconnected system according to claim 1, characterized in that: The formula for calculating the change in mutual impedance between nodes after a fault occurs is: In the formula, Z i ' ,j is the mutual impedance between nodes i and j after the change, Z i,j is the impedance between node i and node j before the fault, Z i,f is the impedance between node i and node f, Z f,j is the impedance between node j and node f, Z f,f is the self-impedance of node f, R f is the resistance of the node.

5. The method for predicting voltage phase jump of a receiving-end power grid of an asynchronous interconnected system according to claim 1, characterized in that: According to the equivalent model of the single-feed AC / DC system after the fault, the expression for solving the equivalent power supply voltage and impedance of the receiving-end power grid is: In the formula, is the commutation bus voltage after the fault, is the equivalent voltage source of the AC system after the fault, is the equivalent impedance of the AC system after the fault, is the current flowing from LCC-HVDC to the AC system after the fault, is the impedance between nodes after the fault. The subscripts CZ, CI, LCC, f and E represent the corresponding node types, i.e., constant impedance load, constant current load, DC feed-in node, fault node and generator node. The bold symbols represent matrices or vectors, and the non-bold symbols represent single elements.

6. A method for predicting voltage phase jump in a receiving-end power grid of an asynchronous interconnected system according to claim 5, characterized in that: The formula for calculating the phase jump of the receiving-end power grid commutation bus voltage is: Δθ=θ L ′ CC -θ LCC =(θ L ′ CC -θ e ′ q +θ e ′ q )-(θ LCC -θ eq +θ eq ); Where Δθ is the phase jump, θ L ' CC ,θ LCC is the voltage phase of the commutation bus, θ e ' q ,θ eq It is the voltage phase of the equivalent voltage source in the AC system.

7. A method for predicting voltage phase jump in a receiving-end power grid of an asynchronous interconnected system according to claim 6, characterized in that: It also includes solving the formula for the phase jump of the receiving-end power grid commutation bus voltage, which is: In the formula, It is the current injected by LCC-HVDC into the receiving grid before the fault.

8. A voltage phase jump prediction system for a receiving-end power grid of an asynchronous interconnected system, characterized in that: A method for predicting voltage phase jumps in a receiving-end power grid of an asynchronous interconnected system according to any one of claims 1 to 7 is applied, comprising: The network equation building module builds the network equation of the receiving-end power grid of the asynchronous interconnected system based on three-phase symmetrical faults; The equivalent model building module obtains the equivalent model of the single-feed AC / DC system before and after the fault according to the network equation of the receiving-end power grid of the asynchronous interconnected system; The equivalent data calculation module solves the equivalent power supply voltage and impedance of the receiving-end power grid based on the equivalent model of the single-feed AC / DC system before the fault; Calculate the change in mutual impedance between nodes after a fault occurs; Based on the equivalent model of the single-infeed AC / DC system after the fault, the equivalent power supply voltage and impedance of the receiving-end power grid are solved; The phase jump result output module calculates the phase jump of the receiving-end power grid commutation bus voltage based on the phase relationship of the equivalent model of the single-feed AC / DC system before and after the fault, based on the equivalent power supply voltage and impedance of the receiving-end power grid before and after the fault and the change in mutual impedance between nodes after the fault occurs.

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