Method and device for analyzing oscillation center in direct current blocking scene

Abstract

The invention discloses a method and a device for analyzing an oscillation center in a direct-current blocking scene, and relates to the technical field of stability analysis of a power system, and the method is characterized in that a physical model of an alternating-current and direct-current tie line parallel system is established; establishing a mathematical model with equivalent direct-current transmission external characteristics, wherein the mathematical model represents the incidence relation between direct-current equivalent parallel resistors connected to the two sides of the alternating-current bus and direct-current active power and the rated voltage of the bus; equivalently simplifying the physical model according to the mathematical model to obtain an equivalent physical model of the AC-DC tie line parallel system, and calculating equivalent potentials on two sides of DC power transmission according to the equivalent physical model; and calculating an equivalent potential amplitude ratio according to the equivalent potentials on the two sides of direct-current power transmission, and substituting the equivalent potential amplitude ratio into an oscillation center position function when the alternating-current and direct-current tie line parallel system is in a direct-current non-locking scene so as to analyze the oscillation center of the alternating-current and direct-current tie line parallel system in the direct-current non-locking scene.

Description

Technical Field

[0001] The present application relates to the technical field of power system stability analysis, and more specifically, to a method and device for analyzing an oscillation center in a DC blocking scenario. Background Art

[0002] As power electronic devices are gradually connected to the power grid in large numbers, their time scale has changed from the electromechanical transient of the traditional power grid to the electromagnetic transient. The dynamic process is becoming faster and the control link is becoming more complex, which has an increasingly prominent impact on the transient stability of the power grid. In particular, the locking problem of high-voltage, high-power DC transmission systems. Once a power electronic device in the DC system fails or stops operating, a large-scale power flow transfer will occur, which may cause the power grid to collapse in severe cases.

[0003] In order to prevent the power system from collapsing after a fault, the power system has set up three lines of defense for fault defense. The third line of defense contains the out-of-step decoupling link, which aims to divide the large system into multiple independent small systems when the large system cannot be kept stable. It is of great significance to prevent the collapse of the power system. However, the access of the DC system has changed the fault characteristics of the traditional power grid to a certain extent, and the important oscillation center determination in the out-of-step decoupling link has become more complicated. If the traditional decoupling strategy is used, it may not be applicable to the AC-DC hybrid system, and may even have a negative effect. Therefore, analyzing the oscillation center migration characteristics of the AC-DC hybrid system will be conducive to formulating a decoupling strategy suitable for the AC-DC hybrid system.

[0004] At present, the existing technology analysis methods for the impact of oscillation center migration mainly include the analysis of the oscillation center migration characteristics of the equivalent two-machine and equivalent three-machine systems without DC out-of-step oscillation and the analysis of the oscillation center migration characteristics of the DC system out-of-step oscillation based on simulation.

[0005] For the analysis of the migration characteristics of the oscillation center without DC out-of-step, the synchronous motor is taken as the main factor, and the analysis of the oscillation center is carried out based on the law of the change of the synchronous motor power angle difference. One of the important conclusions is that the impedance change of the system will cause the change of the oscillation center position. However, the influence of DC transmission on the oscillation center position is not considered in the analysis process, which will lead to inaccurate analysis of the oscillation center position with DC transmission, so it is not suitable for AC / DC hybrid power systems. Summary of the invention

[0006] The purpose of this application is to provide a method and device for analyzing the oscillation center in a DC locking scenario, so as to solve the problem that the prior art does not consider the influence of DC transmission on the oscillation center position, resulting in inaccurate analysis of the oscillation center position containing DC transmission.

[0007] In a first aspect of the present application, a method for analyzing an oscillation center in a DC blocking scenario is provided. The method is applied to an AC / DC tie line parallel system, wherein the AC / DC tie line parallel system is formed by connecting a single AC tie line in parallel with a DC transmission line in an equivalent dual-machine system. The method comprises:

[0008] Establish the physical model of the AC / DC interconnection line parallel system;

[0009] A mathematical model of equivalent external characteristics of DC power transmission is established, wherein the mathematical model represents the relationship between the DC equivalent parallel resistance connected on both sides of the AC bus and the DC active power and the rated voltage of the bus;

[0010] The physical model is simplified equivalently according to the mathematical model to obtain the equivalent physical model of the AC / DC interconnection line parallel system, and the equivalent potential on both sides of the DC transmission is calculated according to the equivalent physical model;

[0011] The equivalent potential amplitude ratio is calculated according to the equivalent potential on both sides of the DC transmission. When the AC / DC interconnection line parallel system is in a DC non-blocking scenario, the equivalent potential amplitude ratio is substituted into the oscillation center position function to analyze the oscillation center of the AC / DC interconnection line parallel system in the DC non-blocking scenario.

[0012] In one implementation, the mathematical model is expressed as:

[0013] Among them, P ref is the DC active power, r N is the DC equivalent parallel resistance connected to the N side of the AC bus, r M is the DC equivalent parallel resistance connected to the AC bus M side, It is the square of the bus rated voltage.

[0014] In one implementation, the physical model is equivalently simplified according to the mathematical model to obtain an equivalent physical model of the AC / DC tie line parallel system, including:

[0015] According to the mathematical model, the external characteristics of the DC transmission part of the physical model are equivalently transformed into a parallel resistor;

[0016] Through the series-parallel transformation of the circuit, the parallel resistance and the impedance on both sides of the AC bus are equivalently transformed with the power supply to obtain the equivalent physical model of the AC / DC tie line parallel system.

[0017] In one implementation, the calculation formula for the equivalent potential on both sides of the DC transmission is:

[0018]

[0019] in, are the equivalent coefficients after adding DC transmission, and are the terminal voltages of the synchronous generator equivalent electromotive force on both sides of the AC bus, r N is the DC equivalent parallel resistance connected to the N side of the AC bus, r M It is the DC equivalent parallel resistance connected to the M side of the AC bus.

[0020] In one implementation, the expression of the oscillation center position function is:

[0021] Among them, δ is the synchronous voltage phase difference on both sides of the AC bus, k e is the equivalent potential amplitude ratio.

[0022] In one implementation, the method further includes:

[0023] When the AC / DC interconnection line parallel system is in a DC blocking scenario, the ratio of the terminal voltages of the equivalent electromotive force of the synchronous generators on both sides of the AC bus is substituted into the oscillation center position function to analyze the oscillation center of the AC / DC interconnection line parallel system in the DC blocking scenario.

[0024] In a second aspect of the present application, an analysis device for an oscillation center in a DC blocking scenario is provided, the device being applied to an AC / DC tie line parallel system, wherein the AC / DC tie line parallel system is formed by connecting a single AC tie line in parallel with a DC transmission line in an equivalent dual-machine system, and the device comprises:

[0025] A physical model building module is used to build a physical model of the AC / DC interconnection line parallel system;

[0026] A mathematical model building module is used to establish a mathematical model of the equivalent external characteristics of direct current transmission, wherein the mathematical model represents the correlation between the direct current equivalent parallel resistance connected on both sides of the AC bus and the direct current active power and the rated voltage of the bus;

[0027] A processing module is used to perform equivalent simplification on the physical model according to the mathematical model, obtain an equivalent physical model of the AC / DC interconnection line parallel system, and calculate the equivalent potential on both sides of the DC transmission according to the equivalent physical model;

[0028] The analysis module is used to calculate the equivalent potential amplitude ratio based on the equivalent potential on both sides of the DC transmission. When the AC / DC interconnection line parallel system is in a DC non-blocking scenario, the equivalent potential amplitude ratio is substituted into the oscillation center position function to analyze the oscillation center of the AC / DC interconnection line parallel system in the DC non-blocking scenario.

[0029] In one implementation, the mathematical model is expressed as:

[0030] Among them, P ref is the DC active power, r N is the DC equivalent parallel resistance connected to the N side of the AC bus, r M is the DC equivalent parallel resistance connected to the AC bus M side, It is the square of the bus rated voltage.

[0031] In one implementation, the processing module is specifically configured to:

[0032] According to the mathematical model, the external characteristics of the DC transmission part of the physical model are equivalently transformed into a parallel resistor;

[0033] Through the series-parallel transformation of the circuit, the parallel resistance and the impedance on both sides of the AC bus are equivalently transformed with the power supply to obtain the equivalent physical model of the AC / DC tie line parallel system.

[0034] In one implementation, the calculation formula for the equivalent potential on both sides of the DC transmission is:

[0035]

[0036] in, are the equivalent coefficients after adding DC transmission, and are the terminal voltages of the synchronous generator equivalent electromotive force on both sides of the AC bus, r N is the DC equivalent parallel resistance connected to the N side of the AC bus, r M It is the DC equivalent parallel resistance connected to the M side of the AC bus.

[0037] Compared with the prior art, this application has the following beneficial effects:

[0038] In an analysis method and device for an oscillation center in a DC blocking scenario provided in an embodiment of the present application, first, an equivalent two-machine system of AC / DC parallel connection is considered as an architecture, and a DC operating characteristic is used as an entry point to establish a mathematical model. The physical model is equivalently simplified in combination with the mathematical model to obtain an equivalent physical model of the AC / DC interconnection line parallel system, thereby equivalently simplifying the external characteristics of the DC interconnection line to a dynamically changing impedance, and then the equivalent potential on both sides of the DC transmission is calculated according to the equivalent physical model, and the equivalent potential amplitude ratio is calculated according to the equivalent potential on both sides of the DC transmission. When the AC / DC interconnection line parallel system is in a DC non-blocking scenario, the equivalent potential amplitude ratio is substituted into the oscillation center position function to analyze the oscillation center of the AC / DC interconnection line parallel system in the DC non-blocking scenario. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] The drawings described herein are used to provide a further understanding of the embodiments of the present application, constitute a part of the present application, and do not constitute a limitation on the embodiments of the present application. In the drawings:

[0040] Figure 1 A schematic flow chart of a method for analyzing an oscillation center in a DC blocking scenario provided in an embodiment of the present application;

[0041] Figure 2 A principle block diagram of a physical model of an AC / DC tie line parallel system provided in an embodiment of the present application;

[0042] Figure 3 An equivalent simplified circuit of the physical model of the AC / DC tie line parallel system provided in the embodiment of the present application;

[0043] Figure 4 A position diagram of the DC blocking oscillation center position changing with the power angle difference provided in an embodiment of the present application;

[0044] Figure 5 A position diagram of the DC non-blocking oscillation center position changing with the power angle difference provided in an embodiment of the present application;

[0045] Figure 6 A principle block diagram of an oscillation center analysis device in a DC blocking scenario provided in an embodiment of the present application. DETAILED DESCRIPTION

[0046] In order to make the objectives, technical solutions and advantages of the present application more clearly understood, the present application is further described in detail below in conjunction with examples and drawings. The illustrative implementation scheme of the present application and its description are only used to explain the present application and are not intended to limit the present application.

[0047] Please refer to Figure 1 , Figure 1 A flow chart of a method for analyzing an oscillation center in a DC blocking scenario provided in an embodiment of the present application is shown in FIG. Figure 1 As shown, the method is applied to an AC / DC tie line parallel system, wherein the AC / DC tie line parallel system is formed by connecting a single AC tie line in parallel with a DC transmission line in an equivalent dual-machine system, and the method comprises:

[0048] S101, establishing a physical model of the AC / DC interconnection line parallel system.

[0049] In this embodiment, if Figure 2 As shown, a physical model of the AC / DC tie line parallel system is established, that is, a single AC tie line is connected in parallel with a DC transmission line in a traditional equivalent dual-machine system.

[0050] exist Figure 2 middle, and are the equivalent electromotive force terminal voltages of the synchronous generators on both sides, assuming Then Z M With Z N are the equivalent internal impedances of the synchronous generators on both sides; Z L is the overall impedance of the AC line, O is a point on the tie line (which can represent the oscillation center position when necessary), and the line impedance is divided into Z L1 With Z L2 Two parts; specify the current on the interconnection line The positive direction is flowing out from M and flowing into N; M and N are AC busbars (nodes); the part in the dotted box is the direct current transmission (DC) part, and the N side is specified as the DC feed-in side.

[0051] S102, establishing a mathematical model of equivalent external characteristics of direct current transmission, wherein the mathematical model represents the correlation between the direct current equivalent parallel resistance connected on both sides of the alternating current bus and the direct current active power and the rated voltage of the bus.

[0052] In this embodiment, the DC power transmission can adjust and transmit active power according to the set value, so the active power transmission is basically not affected by the fluctuation of the power grid, and can be regarded as a constant value in steady-state operation. The transmission power can be represented by the variable resistance R, and the mathematical model of the output power and the variable resistance is established as follows: Among them, P ref is the DC active power, r N is the DC equivalent parallel resistance connected to the N side of the AC bus, r M is the DC equivalent parallel resistance connected to the AC bus M side, It is the square of the bus rated voltage.

[0053] Among them, P ref is the set value of DC active power; is the square of the DC bus voltage. Considering that the voltage amplitudes at different grid connection points are not much different after the fault is removed, It can be approximately regarded as the square of the bus rated voltage; r N The DC equivalent parallel resistance connected to the N side of the AC busbar is a negative sign to indicate active input because it is the DC feed side and the DC can be regarded as a power source. M It is the DC equivalent parallel resistance connected to the M side of the AC bus. Because it is the DC output side, the DC can be regarded as a load, so a positive resistance indicates active consumption.

[0054] S103, performing equivalent simplification on the physical model according to the mathematical model to obtain an equivalent physical model of the AC / DC interconnection line parallel system, and calculating the equivalent potential on both sides of the DC transmission according to the equivalent physical model.

[0055] In this embodiment, according to the equivalent model of the DC part in step S102, the physical model of the AC / DC tie line parallel system in step S101 can be equivalently simplified. The specific steps are as follows: Figure 3 As shown in the figure, the equivalent simplification is as follows: according to the mathematical model, the external characteristics of the DC transmission part of the physical model are equivalently transformed into a parallel resistor; through the series-parallel transformation of the circuit, the parallel resistor and the impedance on both sides of the AC bus and the power supply are equivalently transformed to obtain the equivalent physical model of the AC / DC interconnection line parallel system.

[0056] right Figure 3 The DC part of the original circuit is transformed into a DC equivalent external characteristic to obtain a parallel resistor. Then, through the basic series-parallel transformation of the circuit, the parallel resistor and the system impedance on the left side of M and the right side of N are transformed into an equivalent power supply. Finally, the original circuit is transformed into a traditional equivalent dual-machine system, in which the DC transmission part only affects the equivalent impedance and potential of the systems on both sides. The equivalent potential and resistance can be calculated according to the following formula:

[0057] in, are the equivalent coefficients after adding DC transmission, and are the terminal voltages of the synchronous generator equivalent electromotive force on both sides of the AC bus, r N is the DC equivalent parallel resistance connected to the N side of the AC bus, r M It is the DC equivalent parallel resistance connected to the M side of the AC bus.

[0058] S104, calculating an equivalent potential amplitude ratio based on the equivalent potentials on both sides of the DC transmission, and when the AC / DC interconnection line parallel system is in a DC non-interlocking scenario, substituting the equivalent potential amplitude ratio into an oscillation center position function to analyze the oscillation center of the AC / DC interconnection line parallel system in the DC non-interlocking scenario.

[0059] In this embodiment, when DC is not blocked, DC transmits power, but the system capacity on the AC side is generally multiple times the DC capacity. Therefore, it can be generally considered that the DC equivalent resistance is much larger than the system side resistance. Substituting the equivalent potential of the systems on both sides after equivalent, the oscillation center position can be calculated as follows: in, is the ratio of the equivalent potential amplitudes on both sides of the system.

[0060] like Figure 5 As shown in the figure, the position diagram of the oscillation center changes with the power angle difference when the DC is not locked. The oscillation center appears faster than the traditional power system.

[0061] In some embodiments, the method also includes: when the AC / DC interconnection line parallel system is in a DC locking scenario, substituting the ratio of the terminal voltages of the equivalent electromotive force of the synchronous generator on both sides of the AC bus into the oscillation center position function to analyze the oscillation center of the AC / DC interconnection line parallel system in the DC locking scenario.

[0062] Specifically, in the case of DC blocking, DC does not transmit power, so the DC equivalent resistance is infinite. At this time, the situation degenerates into a traditional equivalent dual-machine system model without DC, and the oscillation center position function is as follows:

[0063]

[0064] in, is the potential amplitude ratio on both sides of the system, and δ is the synchronous voltage phase angle difference on both sides of the system, which can be regarded as the power angle difference of two equal synchronous motors.

[0065] like Figure 4 As shown in the figure, the position diagram of the oscillation center changes with the power angle difference under DC locking conditions. When the potential amplitudes of the systems on both sides are the same, the oscillation center is always at the midpoint of the interconnection line and will not move; when the potential amplitudes of the systems on both sides are different, the oscillation center is only located on the side of the system with lower potential amplitude for a period of time and will not move. At other times, it will continue to change position, but will not reach and exceed the midpoint of the interconnection line.

[0066] Finally, according to the conclusion of DC non-blocking / blocking, the influence of DC blocking on the oscillation center is the speed of occurrence, among which the important influencing factors are the potential amplitude ratio of the two sides of the system, the power angle difference of the two sides of the system, and the equivalent impedance ratio of the AC and DC systems. Secondly, based on the analysis results, the reference factors for the installation of the out-of-step decoupling device are given, that is, if the out-of-step decoupling device needs to be installed in the AC and DC interconnection line parallel system, the above conclusions and the oscillation center function can provide a reference for the site selection of the out-of-step decoupling device.

[0067] Please refer to Figure 6 , Figure 6 A schematic diagram of a device for analyzing an oscillation center in a DC blocking scenario provided in an embodiment of the present application is shown in FIG. Figure 6 As shown, the device is applied to an AC / DC tie line parallel system, wherein the AC / DC tie line parallel system is formed by connecting a single AC tie line in parallel with a DC transmission line in an equivalent dual-machine system, and the device comprises:

[0068] A physical model building module 610 is used to build a physical model of the AC / DC tie line parallel system;

[0069] A mathematical model building module 620 is used to establish a mathematical model of equivalent external characteristics of direct current transmission, wherein the mathematical model represents the correlation between the direct current equivalent parallel resistance connected on both sides of the alternating current bus and the direct current active power and the rated voltage of the bus;

[0070] The processing module 630 is used to perform equivalent simplification on the physical model according to the mathematical model, obtain an equivalent physical model of the AC / DC tie line parallel system, and calculate the equivalent potential on both sides of the DC transmission according to the equivalent physical model;

[0071] The analysis module 640 is used to calculate the equivalent potential amplitude ratio according to the equivalent potential on both sides of the DC transmission, and when the AC / DC interconnection line parallel system is in a DC non-blocking scenario, substitute the equivalent potential amplitude ratio into the oscillation center position function to analyze the oscillation center of the AC / DC interconnection line parallel system in the DC non-blocking scenario.

[0072] It can be seen that the analysis device of the oscillation center in the DC blocking scenario provided in the embodiment of the present application is similar to the above Figure 1 The method for analyzing the oscillation center in a DC locking scenario shown is a technical solution based on the same inventive concept. Through the detailed description of the method for analyzing the oscillation center in a DC locking scenario provided in the above embodiment, technical personnel in this field can clearly understand the implementation process of the device for analyzing the oscillation center in a DC locking scenario in this embodiment. Therefore, for the sake of conciseness of the specification, it will not be repeated here.

[0073] Accordingly, an embodiment of the present application provides a multi-point control device for a pipeline under ultra-high voltage direct current interference. First, an equivalent two-machine system of AC and DC parallel connection is considered as an architecture, and DC operating characteristics are used as an entry point to establish a mathematical model. The physical model is equivalently simplified in combination with the mathematical model to obtain an equivalent physical model of the AC and DC interconnection line parallel system, thereby equivalently simplifying the external characteristics of the DC interconnection line to a dynamically changing impedance, and then the equivalent potential on both sides of the DC transmission is calculated according to the equivalent physical model, and the equivalent potential amplitude ratio is calculated according to the equivalent potential on both sides of the DC transmission. When the AC and DC interconnection line parallel system is in a DC non-blocking scenario, the equivalent potential amplitude ratio is substituted into the oscillation center position function to analyze the oscillation center of the AC and DC interconnection line parallel system in the DC non-blocking scenario.

[0074] In some embodiments, the mathematical model is expressed as: Among them, P ref is the DC active power, r N is the DC equivalent parallel resistance connected to the N side of the AC bus, r M is the DC equivalent parallel resistance connected to the AC bus M side, It is the square of the bus rated voltage.

[0075] In some embodiments, the processing module is specifically configured to:

[0076] According to the mathematical model, the external characteristics of the DC transmission part of the physical model are equivalently transformed into a parallel resistor;

[0077] Through the series-parallel transformation of the circuit, the parallel resistance and the impedance on both sides of the AC bus are equivalently transformed with the power supply to obtain the equivalent physical model of the AC / DC tie line parallel system.

[0078] In some embodiments, the calculation formula for the equivalent potential on both sides of the DC transmission is:

[0079]

[0080] in, are the equivalent coefficients after adding DC transmission, and are the terminal voltages of the synchronous generator equivalent electromotive force on both sides of the AC bus, r N is the DC equivalent parallel resistance connected to the N side of the AC bus, r M It is the DC equivalent parallel resistance connected to the M side of the AC bus.

[0081] The specific implementation methods described above further illustrate the purpose, technical solutions and beneficial effects of the present application in detail. It should be understood that the above description is only the specific implementation method of the present application and is not intended to limit the scope of protection of the present application. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present application should be included in the scope of protection of the present application.

Claims

1. A method for analyzing the oscillation center in a DC blocking scenario, characterized in that: The method is applied to an AC / DC tie line parallel system, wherein the AC / DC tie line parallel system is formed by connecting a single AC tie line in parallel with a DC transmission line in an equivalent dual-machine system, and the method comprises: Establish the physical model of the AC / DC interconnection line parallel system; A mathematical model of equivalent external characteristics of DC power transmission is established, wherein the mathematical model represents the relationship between the DC equivalent parallel resistance connected on both sides of the AC bus and the DC active power and the rated voltage of the bus; The physical model is simplified equivalently according to the mathematical model to obtain the equivalent physical model of the AC / DC interconnection line parallel system, and the equivalent potential on both sides of the DC transmission is calculated according to the equivalent physical model; The equivalent potential amplitude ratio is calculated according to the equivalent potential on both sides of the DC transmission. When the AC / DC interconnection line parallel system is in a DC non-blocking scenario, the equivalent potential amplitude ratio is substituted into the oscillation center position function to analyze the oscillation center of the AC / DC interconnection line parallel system in the DC non-blocking scenario.

2. The method according to claim 1, characterized in that The mathematical model is expressed as: Among them, P ref is the DC active power, r N is the DC equivalent parallel resistance connected to the N side of the AC bus, r M is the DC equivalent parallel resistance connected to the AC bus M side, It is the square of the bus rated voltage.

3. The method according to claim 1, characterized in that The physical model is simplified equivalently according to the mathematical model to obtain the equivalent physical model of the AC / DC tie line parallel system, including: According to the mathematical model, the external characteristics of the DC transmission part of the physical model are equivalently transformed into a parallel resistor; Through the series-parallel transformation of the circuit, the parallel resistance and the impedance on both sides of the AC bus are equivalently transformed with the power supply to obtain the equivalent physical model of the AC / DC tie line parallel system.

4. The method according to claim 3, characterized in that The calculation formula of the equivalent potential on both sides of the DC transmission is: in, are the equivalent coefficients after adding DC transmission, and are the terminal voltages of the synchronous generator equivalent electromotive force on both sides of the AC bus, r N is the DC equivalent parallel resistance connected to the N side of the AC bus, r M It is the DC equivalent parallel resistance connected to the M side of the AC bus.

5. The method according to claim 1, characterized in that The expression of the oscillation center position function is: Among them, δ is the synchronous voltage phase difference on both sides of the AC bus, k e is the equivalent potential amplitude ratio.

6. The method according to claim 1, characterized in that The method also includes: When the AC / DC interconnection line parallel system is in a DC blocking scenario, the ratio of the terminal voltages of the equivalent electromotive force of the synchronous generators on both sides of the AC bus is substituted into the oscillation center position function to analyze the oscillation center of the AC / DC interconnection line parallel system in the DC blocking scenario.

7. An analysis device for the oscillation center in a DC blocking scenario, characterized in that: The device is applied to an AC / DC tie line parallel system, wherein the AC / DC tie line parallel system is formed by connecting a single AC tie line in parallel with a DC transmission line in an equivalent dual-machine system, and the device comprises: A physical model building module is used to build a physical model of the AC / DC interconnection line parallel system; A mathematical model building module is used to establish a mathematical model of the equivalent external characteristics of direct current transmission, wherein the mathematical model represents the correlation between the direct current equivalent parallel resistance connected on both sides of the AC bus and the direct current active power and the rated voltage of the bus; A processing module is used to perform equivalent simplification on the physical model according to the mathematical model, obtain an equivalent physical model of the AC / DC interconnection line parallel system, and calculate the equivalent potential on both sides of the DC transmission according to the equivalent physical model; The analysis module is used to calculate the equivalent potential amplitude ratio based on the equivalent potential on both sides of the DC transmission. When the AC / DC interconnection line parallel system is in a DC non-blocking scenario, the equivalent potential amplitude ratio is substituted into the oscillation center position function to analyze the oscillation center of the AC / DC interconnection line parallel system in the DC non-blocking scenario.

8. The device according to claim 7, characterized in that The mathematical model is expressed as: Among them, P ref is the DC active power, r N is the DC equivalent parallel resistance connected to the N side of the AC bus, r M is the DC equivalent parallel resistance connected to the AC bus M side, It is the square of the bus rated voltage.

9. The device according to claim 7, characterized in that Processing module, specifically used for: According to the mathematical model, the external characteristics of the DC transmission part of the physical model are equivalently transformed into a parallel resistor; Through the series-parallel transformation of the circuit, the parallel resistance and the impedance on both sides of the AC bus are equivalently transformed with the power supply to obtain the equivalent physical model of the AC / DC tie line parallel system.

10. The device according to claim 9, characterized in that The calculation formula of the equivalent potential on both sides of the DC transmission is: in, are the equivalent coefficients after adding DC transmission, and are the terminal voltages of the synchronous generator equivalent electromotive force on both sides of the AC bus, r N is the DC equivalent parallel resistance connected to the N side of the AC bus, r M It is the DC equivalent parallel resistance connected to the M side of the AC bus.

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