A method and system for predicting voltage phase jump in receiving-end power grid of asynchronous interconnected system

Abstract

The present invention discloses a method and system for predicting voltage phase jumps in a receiving-end power grid of an asynchronous interconnected system, relating to the field of electric power engineering technology. A network equation is established based on the composition structure, distribution characteristics, and transient characteristics of the receiving-end power grid components of the asynchronous interconnected system to accurately reflect the electrical behavior of the commutation bus phase of the asynchronous interconnected system under different fault conditions. Based on the network equation of the receiving-end power grid of the asynchronous interconnected system, an equivalent model of a single-feed AC / DC system before and after the fault is obtained. The equivalent power supply voltage and impedance of the receiving-end power grid before and after the fault, as well as the mutual impedance change between nodes after the fault, are solved. Finally, based on the phase relationship of the equivalent model of the single-feed AC / DC system before and after the fault, the phase jump of the commutation bus voltage of the receiving-end power grid is calculated. This solves the problem in the prior art that the quantification method for phase jumps is not accurate enough or cannot reflect the dynamic characteristics of phase changes, thereby providing a strong basis for system fault analysis, state monitoring, and dynamic scheduling.

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] With the rapid economic and social development of the world, the demand for high-capacity, long-distance power transmission is growing daily, driving the widespread application of conventional direct current (UHVDC) transmission systems worldwide. In some regions, 19 ultra-high voltage direct current (UHVDC) transmission lines have been completed for east-west power transmission, with a total transmission capacity exceeding 270 million kW. The power grid is gradually shifting from a large synchronous grid to an asynchronous interconnected grid architecture. At the same time, the proportion of renewable energy generators in the power grid is increasing. Both LCC-HVDC and renewable energy generators rely on power electronics as key technologies. The fast shutdown and nonlinear characteristics of power electronics make power system failures more complex and severe, leading to risks.

[0003] Phase jump is another important characteristic of voltage sag, in addition to residual voltage and fault duration. Previous research has found that phase jump angles can affect the synchronization of grid-following inverters with the grid, cause distributed photovoltaic power curtailment and generator tripping, and induce rotor overcurrent in doubly-fed wind turbines, thereby threatening the fault ride-through capability of renewable energy power plants and the stable operation of power systems. However, phase jump remains understudied, and its magnitude remains unknown, requiring further research to quantify.

[0004] Therefore, how to accurately quantify the voltage phase jump of the receiving-end power grid of the asynchronous interconnected system is an urgent problem that needs to be solved by those skilled in the art. Summary of the Invention

[0005] In view of this, the present invention provides a method and system for predicting voltage phase jumps in 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 solutions:

[0007] A method for predicting voltage phase jumps in 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-infeed AC / DC system before the fault, the equivalent power supply voltage and impedance of the receiving-end power grid are solved;

[0011] Calculate the mutual impedance change 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-end power grid before and after the fault, as well as the mutual impedance change between nodes after the fault, the phase jump of the receiving-end power grid commutation bus voltage is calculated according to the phase relationship of the equivalent model of the single-infeed 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] Where, 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 indicate 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.

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

[0018] Performing matrix calculation on the network equation of the receiving-end power grid of the asynchronous interconnected system, the following equation is obtained:

[0019]

[0020] Combining the two equations above, we can get the expression of the equivalent model of the single-infeed 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] Where Z i ' ,j is the mutual impedance between nodes i and j after the change, Z i,j is the impedance between nodes i and 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-infeed 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] Where, 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.

[0029] Optionally, the formula for calculating the phase jump of the receiving-end power grid commutation bus voltage 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 is the voltage phase of the equivalent voltage source in the AC system.

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

[0033] θ L ' LCC -θ e 'q ≈0;

[0034]

[0035] Where, It is the current injected into the receiving grid by LCC-HVDC 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-infeed AC / DC system before and after the fault based on 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-infeed AC / DC system before the fault;

[0040] Calculate the mutual impedance change 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 single-infeed AC / DC system equivalent model before and after the fault, based on the equivalent power source voltage and impedance of the receiving-end power grid before and after the fault, as well as the change in mutual impedance between nodes after the fault occurs.

[0043] It can be seen from the above technical solution that, compared with the prior art, the present invention discloses a method and system for predicting voltage phase jumps in the receiving-end power grid of an asynchronous interconnected system. A network equation is established based on the composition structure, distribution characteristics and transient characteristics of the receiving-end power grid components of the asynchronous interconnected system to accurately reflect the electrical behavior of the commutation bus phase of the asynchronous interconnected system under different fault conditions. A quantitative analysis method for phase jumps is proposed to solve 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, thereby providing 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 following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are merely embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying any creative work.

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

[0046] Figure 2 This is a schematic diagram of the equivalent model structure 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 Schematic diagram of the 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; Figure 8 (a) Figure 8 (b) Figure 8 (c) shows the calculation results of Case 1, Case 2, and Case 3 respectively;

[0055] Figure 9 This is a flow chart of calculating the voltage phase jump value provided by the present invention. DETAILED DESCRIPTION

[0056] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0057] An embodiment of the present invention discloses a method for predicting voltage phase jumps in 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-infeed AC / DC system before the fault, the equivalent power supply voltage and impedance of the receiving-end power grid are solved;

[0061] Calculate the mutual impedance change 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-end power grid before and after the fault, as well as the mutual impedance change between nodes after the fault, the phase jump of the receiving-end power grid commutation bus voltage is calculated according to the phase relationship of the equivalent model of the single-infeed 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 connected via high-voltage direct current (HVDC) transmission technology. Due to the decoupling characteristics of DC transmission, the interconnected grids can operate at different frequencies. LCC-HVDC is the most common HVDC transmission technology used in asynchronous interconnected systems.

[0066] The receiving 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 loads (CI1, CI2, ..., CI n ) and other components. Figure 1In the receiving grid, the 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 to be 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 feed-in 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 detect the voltage phase jump of an asymmetric fault. However, a symmetric fault will cause a phase jump in the voltage of all phases, thus posing the greatest threat to the DC system. Therefore, the model is established based on a three-phase symmetric fault. 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] Where, 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 indicate 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.

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

[0074] Based on the receiving-end grid network equation of the asynchronous interconnected system shown in formula (1), formula (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 grid commutation busbar, E eq Is the equivalent power supply voltage of the receiving end grid. eq and X eq are the resistance and reactance of the equivalent system, and θ LCC and θ eq Represents 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 Q absorbed by the inverter is d is also zero, as shown in formula (4), where 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 generated 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) 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 Equation (5) due to the grounding of node f. Similarly, the process of connecting the CLCC to the AC system can also be modified according to Equation (5).

[0081]

[0082] Where Z i ' ,j is the mutual impedance between nodes i and j after the change, Z i,j is the impedance between nodes i and 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 obtained after considering the fault R f and C LCC formed after the changes.

[0084]

[0085] Where, 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.

[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 is the voltage phase of the equivalent voltage source in the AC system.

[0091] When 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] Where, It is the current injected into the receiving grid by LCC-HVDC before the fault.

[0095] According to equation (9), the phase jump Δθ consists of two main parts in the formula, which are 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) arises from the transient change in DC power flow caused by the fault. Although the sending-end grid fault does not affect the network structure of the receiving-end grid, it still causes a phase jump in the receiving-end grid converter bus by changing the DC power flow. Therefore, the conclusion drawn from equation (9) also applies to the sending-end grid fault, 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's commutation bus voltage. By considering network characteristics and modeling LCC-HVDC based on its power characteristics, the proposed single-infeed 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 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 model for analyzing voltage phase jumps. However, this model is only applicable to radial distribution networks and is not suitable for network-structured transmission systems. Furthermore, this method ignores load current, which plays a significant role in actual power systems. This method also suffers from 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 here was used as the receiving-end grid. To incorporate constant-current loads for verification, the loads at seven nodes in the original system were replaced with constant-current loads, representing 44.72% of the total system load. Other parameters, such as transmission lines, load levels, generator parameters, and transformer parameters, remained consistent with those of the standard IEEE 39-bus system.

[0106] LCC-HVDC system that realizes asynchronous interconnection of systems Figure 7 ,in Figure 7 (a) is the LCC-HVDC system of Model 1, Figure 7 (b) shows the LCC-HVDC system of Model 2. This LCC-HVDC system is based on the CIGRE LCC-HVDC benchmark system. In this model, the equivalent Thevenin system is replaced with a transmission line with an impedance of 0.0529 + j0.529 (Ω / km). All other system parameters remain 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 has the inverter station connected to node 38, and the transformer between nodes 29 and 38 replaced with a 10-kilometer transmission line.

[0109] Model 2: LCC-HVDC feed-in at point 2 Figure 6 The receiving grid is shown, with the inverter station connected to node 30 and the transformer between nodes 02 and 30 replaced by a 10-kilometer transmission line. To balance the active power provided by the DC system, generator G8 and its corresponding transformer were 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 receiving-end three-phase fault at the odd nodes and node 38 (DC feed-in node) of model 1, R f =0.1Ω.

[0113] Case 2: Set a three-phase fault at the receiving end at the even-numbered nodes and node 30 (DC feed-in node) of model 2, with 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 case 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°, where the maximum absolute error occurs at node 29. Due to the failure of node 29, Δθ cal =-96.713°, Δθ mea =-101.037°, with a relative error of 4.230%. This relative error is very small and falls within an acceptable range, which is acceptable when predicting the impact of phase jump on CFFR.

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

[0118] according to Figure 8 (c), with R f The increase of θ PAJ In Case 3, different R f The error range of the value is 0.380° to 3.725°, and the maximum absolute error occurs in 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%, which is 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, in Case 3, R 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 The RMS value of Δθ mea The RMS values ​​of the two 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 noticeable 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 can 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 use the network structure to obtain the AC voltage phase jump value of the commutation bus of the asynchronous interconnected receiving-end power grid. Since modern power systems are equipped with a large number of measurement and detection equipment, information such as the network topology and load composition 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 as an example, the network topology, CZ load and other relevant data of model 3 are first input 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) used in this embodiment is as follows Figure 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-infeed AC / DC system before and after the fault based on 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-infeed AC / DC system before the fault;

[0129] Calculate the mutual impedance change 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 single-infeed AC / DC system equivalent model before and after the fault, based on the equivalent power source voltage and impedance of the receiving-end power grid before and after the fault, as well as the change in mutual impedance between nodes after the fault occurs.

[0132] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. Reference can be made to the common and similar parts between the various embodiments. For the devices disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the description is relatively simple, and the relevant parts can be referred to the method description.

[0133] The above description of the disclosed embodiments is intended to enable one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily 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 is not limited to the embodiments shown herein but is intended to conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for predicting voltage phase jumps in 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-infeed AC / DC system before the fault, the equivalent power supply voltage and impedance of the receiving-end power grid are solved; Calculate the mutual impedance change 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-end grid before and after the fault, as well as the mutual impedance change between nodes after the fault, the phase jump of the receiving-end grid commutation bus voltage is calculated according to the phase relationship of the equivalent model of the single-infeed AC / DC system before and after the fault. The formula for calculating the phase jump of the receiving-end power grid commutation bus voltage is: Δθ=θ′ LCC -θ LCC =(θ′ LCC -θ′ eq +θ′ eq )-(θ LCC -θ eq +θ eq ); Where Δθ is the phase jump, θ′ LCC ,θ LCC is the voltage phase of the commutation bus, θ′ eq ,θ eq is the voltage phase of the equivalent voltage source in the AC system; It also includes solving the formula for the phase jump of the receiving-end power grid commutation bus voltage, specifically: θ′ LCC -θ′ eq ≈0; Where, is the equivalent power supply voltage of the receiving-end power grid; is the equivalent impedance of the AC system; is the equivalent voltage source of the AC system after the fault, It is the current injected into the receiving grid by LCC-HVDC before the fault.

2. 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 network equation of the receiving-end power grid of the asynchronous interconnected system is specifically: Where, 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 indicate 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.

3. The method for predicting voltage phase jump of a receiving-end power grid of an asynchronous interconnected system according to claim 2, 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-infeed AC / DC system before and after the fault is obtained as follows: Performing matrix calculation on the network equation of the receiving-end power grid of the asynchronous interconnected system, the following equation is obtained: Combining the two equations above, we can get the expression of the equivalent model of the single-infeed 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: Where Z′ i,j is the mutual impedance between nodes i and j after the change, Z i,j is the impedance between nodes i and 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 node f.

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: Based on the equivalent model of the single-infeed AC / DC system after the fault, the expressions for solving the equivalent power supply voltage and impedance of the receiving-end power grid are: Where, 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 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 5 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-infeed AC / DC system before and after the fault based on 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-infeed AC / DC system before the fault; Calculate the mutual impedance change 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 single-infeed AC / DC system equivalent model before and after the fault, based on the equivalent power source voltage and impedance of the receiving-end power grid before and after the fault, as well as the change in mutual impedance between nodes after the fault occurs.

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