Analysis method and device for oscillation center in DC blocking scenario

Abstract

The present application discloses an analysis method and device for an oscillation center in a DC blocking scenario, which relates to the technical field of power system stability analysis. The key points of its technical solution are as follows: establishing a physical model of an AC-DC tie line parallel system; establishing a mathematical model for equivalent external characteristics of DC transmission, where the mathematical model characterizes the correlation relationship between the equivalent parallel resistance of DC connected to both sides of the AC bus, the DC active power, and the rated voltage of the bus; performing equivalent simplification on the physical model according to the mathematical model to obtain an equivalent physical model of the AC-DC tie line parallel system, calculating the equivalent electromotive forces on both sides of DC transmission according to the equivalent physical model; calculating the ratio of the amplitudes of the equivalent electromotive forces, and when the AC-DC tie line parallel system is in a non-DC blocking scenario, substituting the ratio of the amplitudes of the equivalent electromotive forces into the oscillation center position function to analyze the oscillation center of the AC-DC tie line parallel system in the non-DC blocking scenario.

Description

Technical Field

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

[0002] With the gradual large-scale access of power electronic devices to the power grid, the time scale changes from the electromechanical transient of the traditional power grid to the electromagnetic transient. The dynamic process is faster and the control links are more complex, and the impact on the transient stability of the power grid is becoming more prominent. Especially for the blocking problem of high-voltage and high-power DC transmission systems, once a fault occurs or the power electronic devices in the DC system stop operating, a large-scale power flow transfer will occur, and in severe cases, it may lead to the collapse of the power grid.

[0003] To prevent the power system from collapsing after a fault, the power system has set up three lines of defense for fault prevention. The third line of defense contains an out-of-step splitting link, aiming to divide the large system into multiple independent small systems when the large system cannot maintain stability, which is of great significance for preventing 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 determination of the important oscillation center in the out-of-step splitting link has become more complex. If the traditional splitting strategy is used, it may not be applicable to the AC-DC hybrid system, and even have negative effects. Therefore, analyzing the oscillation center migration characteristics of the AC-DC hybrid system will be beneficial to formulating a splitting strategy applicable to the AC-DC hybrid system.

[0004] Currently, the existing analysis methods for the influence of oscillation center migration mainly include the analysis of the migration characteristics of the non-DC out-of-step oscillation center based on the equivalent two-machine and equivalent three-machine systems and the analysis of the migration characteristics of the out-of-step oscillation center with a DC system based on simulation.

[0005] For the analysis of the migration characteristics of the non-DC out-of-step oscillation center, it is mainly based on synchronous motors and analyzes the oscillation center based on the change law of the power angle difference of synchronous motors. One of its important conclusions is that the change of the system impedance will cause the change of the oscillation center position. However, the influence of DC transmission on the oscillation center position is not considered in this analysis process, which will lead to inaccurate analysis of the oscillation center position with DC transmission. Therefore, it is not applicable to the AC-DC hybrid power system. Summary of the Invention

[0006] The purpose of the present application is to provide a method and device for analyzing the oscillation center in a DC blocking scenario, so as to solve the problem that the existing technology does not consider the influence of DC transmission on the oscillation center position, which will lead to inaccurate analysis of the oscillation center position with DC transmission.

[0007] In the first aspect of the present application, a method for analyzing the oscillation center in the DC blocking scenario is provided. The method is applied to an AC-DC tie-line parallel system, and 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 two-machine system. The method includes:

[0008] Establish a physical model of the AC-DC tie-line parallel system;

[0009] Establish a mathematical model equivalent to the external characteristics of DC transmission, where the mathematical model characterizes the correlation between the DC equivalent parallel resistors connected to both sides of the AC bus, the DC active power, and the rated voltage of the bus;

[0010] According to the mathematical model, perform equivalent simplification on the physical model to obtain an equivalent physical model of the AC-DC tie-line parallel system, and calculate the equivalent electromotive forces on both sides of the DC transmission according to the equivalent physical model;

[0011] Calculate the ratio of the magnitudes of the equivalent electromotive forces according to the equivalent electromotive forces on both sides of the DC transmission. When the AC-DC tie-line parallel system is in the DC non-blocking scenario, substitute the ratio of the magnitudes of the equivalent electromotive forces into the oscillation center position function to analyze the oscillation center of the AC-DC tie-line parallel system in the DC non-blocking scenario.

[0012] In one implementation, the expression of the mathematical model is:

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

[0014] In one implementation, according to the mathematical model, performing equivalent simplification on the physical model to obtain an equivalent physical model of the AC-DC tie-line parallel system includes:

[0015] According to the mathematical model, perform an equivalent transformation on the external characteristics of the DC transmission part of the physical model to a parallel resistor;

[0016] Through circuit series-parallel transformation, perform equivalent transformation on the parallel resistor, the impedances on both sides of the AC bus, and the power supply to obtain an equivalent physical model of the AC-DC tie-line parallel system.

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

[0018]

[0019] where, They are the equivalent coefficients after adding HVDC transmission respectively, and They are the terminal voltages of the equivalent electromotive forces of the synchronous generators on both sides of the AC bus respectively, r N is the DC equivalent shunt resistance connected to the N side of the AC bus, r M is the DC equivalent shunt resistance connected to the M side of the AC bus.

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

[0021] where δ is the phase angle difference of the synchronous voltages on both sides of the AC bus, k e is the equivalent electromotive force amplitude ratio.

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

[0023] When the AC-DC tie-line parallel system is in the DC blocking scenario, substitute the ratio of the terminal voltages of the equivalent electromotive forces of the synchronous generators on both sides of the AC bus into the oscillation center position function to analyze the oscillation center of the AC-DC tie-line parallel system in the DC blocking scenario.

[0024] In the second aspect of the present application, an analysis device for the oscillation center in the DC blocking scenario is provided. The device is applied to the AC-DC tie-line parallel system, and the AC-DC tie-line parallel system is formed by paralleling a single AC tie-line with a DC transmission line in an equivalent two-machine system. The device includes:

[0025] A physical model construction module for establishing a physical model of the AC-DC tie-line parallel system;

[0026] A mathematical model construction module for establishing a mathematical model equivalent to the external characteristics of HVDC transmission, where the mathematical model characterizes the correlation between the DC equivalent shunt resistances connected to both sides of the AC bus, the DC active power, and the rated voltage of the bus;

[0027] A processing module for 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 the equivalent electromotive forces on both sides of the HVDC transmission according to the equivalent physical model;

[0028] An analysis module for calculating the equivalent electromotive force amplitude ratio according to the equivalent electromotive forces on both sides of the HVDC transmission. When the AC-DC tie-line parallel system is in the DC non-blocking scenario, substitute the equivalent electromotive force amplitude ratio into the oscillation center position function to analyze the oscillation center of the AC-DC tie-line parallel system in the DC non-blocking scenario.

[0029] In one implementation, the expression of the mathematical model is:

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

[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 resistance;

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

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

[0035]

[0036] Among them, are the equivalent coefficients after adding DC transmission respectively, and are the terminal voltages of the equivalent electromotive forces of the synchronous generators on both sides of the AC bus respectively, and r N is the DC equivalent parallel resistance connected to the N side of the AC bus, and r M is the DC equivalent parallel resistance connected to the M side of the AC bus.

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

[0038] In the analysis method and device for the oscillation center in a DC blocking scenario provided in the embodiments of the present application, first, considering the equivalent two-machine system with AC-DC parallel connection as the architecture and taking the DC operating characteristics as the starting point, a mathematical model is established. Combining the mathematical model, the physical model is equivalently simplified to obtain the equivalent physical model of the AC-DC tie line parallel system, so as to equivalently transform the external characteristics of the DC tie line into a dynamically changing impedance. Then, according to the equivalent physical model, the equivalent electromotive forces on both sides of the DC transmission are calculated, and the ratio of the equivalent electromotive force amplitudes is calculated based on the equivalent electromotive forces on both sides of the DC transmission. When the AC-DC tie line parallel system is in a DC non-blocking scenario, the ratio of the equivalent electromotive force amplitudes is substituted into the oscillation center position function to analyze the oscillation center of the AC-DC tie line parallel system in the DC non-blocking scenario. Description of the Drawings

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

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

[0041] Figure 2 It is a principle block diagram of a physical model of an AC-DC tie line parallel system provided by an embodiment of the present application;

[0042] Figure 3 It is an equivalent simplified circuit of a physical model of an AC-DC tie line parallel system provided by an embodiment of the present application;

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

[0044] Figure 5 It is a position diagram of the oscillation center position changing with the power angle difference when the DC is not blocked provided by an embodiment of the present application;

[0045] Figure 6 It is a principle block diagram of an analysis device for an oscillation center in a DC blocking scenario provided by an embodiment of the present application. Detailed implementation manners

[0046] To make the objectives, technical solutions, and advantages of the present application clearer and more understandable, the present application will be further described in detail below in conjunction with the embodiments and the accompanying drawings. The illustrative embodiments of the present application and their descriptions are only used to explain the present application and do not limit the present application.

[0047] Please refer to Figure 1 , Figure 1 It is a schematic flow chart of an analysis method for an oscillation center in a DC blocking scenario provided by an embodiment of the present application. As shown in Figure 1 , the method is applied to an AC-DC tie line parallel system, and the AC-DC tie line parallel system is formed by paralleling a single AC tie line with a DC transmission line in an equivalent two-machine system. The method includes:

[0048] S101, establish a physical model of the AC-DC tie line parallel system.

[0049] In this embodiment, as shown in Figure 2 , establish a physical model of the AC-DC tie line parallel system, that is, parallel a single AC tie line with a DC transmission line in a traditional equivalent two-machine system.

[0050] In Figure 2 , And are the terminal voltages of the equivalent electromotive forces of the synchronous generators on both sides respectively. Assume that Then Z M and Z N are the equivalent internal impedances of the synchronous generators on both sides respectively; Z L is the overall impedance of the AC line, O is a point on the tie line (the position of the oscillation center can be represented when needed). At this time, the line impedance is divided into Z L1 and Z L2 two parts; it is stipulated that the positive direction of the current on the tie line is flowing out from M and flowing into N; M and N are AC buses (nodes); the part in the dashed box is the DC transmission (DC) part, and it is stipulated that the N side is the DC feeding side.

[0051] S102. Establish a mathematical model equivalent to the external characteristics of DC transmission, where the mathematical model characterizes the correlation between the equivalent parallel resistors connected to both sides of the AC bus, the DC active power, and the rated voltage of the bus.

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

[0053] where P ref is the set value of the DC active power; is the square of the voltage of the DC landing bus. Considering that the voltage amplitudes at different parallel connection points are not very different after the fault is removed, so can be approximately regarded as the square of the rated voltage of the bus; r N is the equivalent parallel resistor connected to the N side of the AC bus for DC. Since it is the DC feeding side and the DC can be regarded as a power source, the resistor needs to be added with a negative sign to represent the active power input; r M is the equivalent parallel resistor connected to the M side of the AC bus for DC. Since it is the DC output side and the DC can be regarded as a load, the resistor is positive to represent the active power consumption.

[0054] S103. According to the mathematical model, perform equivalent simplification on the physical model to obtain the equivalent physical model of the AC-DC tie line parallel system, and calculate the equivalent electromotive forces on both sides of the DC transmission according to the equivalent physical model.

[0055] In this embodiment, based on 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 Figure 3 shown. The equivalent simplification is specifically 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 circuit series-parallel transformation, the parallel resistor, the impedances on both sides of the AC bus, and the power sources are equivalently transformed to obtain the equivalent physical model of the AC-DC tie line parallel system.

[0056] Perform a DC equivalent transformation of the external characteristics on the DC part of the original circuit in Figure 3 to obtain a parallel resistor. Then, through basic circuit series-parallel transformation, the parallel resistor, the system impedances and power sources on the left side of M and the right side of N are equivalently transformed. Finally, the original circuit is equivalently transformed into a traditional equivalent two-machine system. The DC transmission part only affects the equivalent impedances and electromotive forces of the two sides of the system. The equivalent electromotive force and resistance can be calculated according to the following formula:

[0057] where, are the equivalent coefficients after adding DC transmission respectively, and are the terminal voltages of the equivalent electromotive forces of the synchronous generators on both sides of the AC bus respectively. r N is the DC equivalent parallel resistor connected to the N side of the AC bus, and r M is the DC equivalent parallel resistor connected to the M side of the AC bus.

[0058] S104. Calculate the equivalent electromotive force amplitude ratio according to the equivalent electromotive forces on both sides of the DC transmission. When the AC-DC tie line parallel system is in the DC non-blocking scenario, substitute the equivalent electromotive force amplitude ratio into the oscillation center position function to analyze the oscillation center of the AC-DC tie line parallel system in the DC non-blocking scenario.

[0059] In this embodiment, in the case of DC non-blocking, the DC transmission power is, but the AC side system capacity is generally multiple times that of the DC capacity. Therefore, it can generally be considered that the DC equivalent resistance is much larger than the system side resistance. Substitute the equivalent electromotive forces of the two sides of the system after equivalence, and the oscillation center position can be calculated as follows: where, is the equivalent electromotive force amplitude ratio of the two sides of the system.

[0060] As Figure 5 shown, the position diagram of the oscillation center changing with the power angle difference in the case of DC non-blocking. The speed at which the oscillation center appears is faster than that of the traditional power system.

[0061] In some embodiments, the method further includes: when the AC-DC tie-line parallel system is in a DC blocking scenario, substituting the ratio of the terminal voltages of the equivalent electromotive forces of the synchronous generators on both sides of the AC bus into the oscillation center position function to analyze the oscillation center of the AC-DC tie-line parallel system in the DC blocking scenario.

[0062] Specifically, in the case of DC blocking, no power is transmitted by the DC, so the DC equivalent resistance is infinite. At this time, the situation degenerates into a traditional equivalent two-machine system model without DC. The oscillation center position function is as follows:

[0063]

[0064] where is the ratio of the potential amplitudes on both sides of the system, δ is the phase angle difference of the synchronous voltages on both sides of the system, which can be regarded as the power angle difference between the two equivalent synchronous machines.

[0065] As Figure 4 shown, it is a position diagram of the oscillation center changing with the power angle difference in the case of DC blocking. When the potential amplitudes of the two sides of the system are the same, the oscillation center is always at the midpoint of the tie-line and does not move; when the potential amplitudes of the two sides of the system are different, the oscillation center is only stationary on the side of the system with a lower potential amplitude for a certain period of time, and will change its position continuously at other times, but will not reach and exceed the midpoint of the tie-line.

[0066] Finally, based on the conclusions of the DC non-blocking / blocking cases, the influence of DC blocking on the oscillation center is the speed of occurrence. The important influencing factors are the ratio of the potential amplitudes of the two sides of the system, the power angle difference between the two sides of the system, and the ratio of the equivalent impedances of the AC-DC systems. Secondly, based on the analysis results, reference elements for installing the out-of-step splitting device are also given, that is, if the out-of-step splitting device needs to be installed in the AC-DC tie-line parallel system, the above conclusions and the oscillation center function can be used as a reference for the location selection of the out-of-step splitting device.

[0067] Please refer to Figure 6 , Figure 6 which is a principle block diagram of an analysis device for the oscillation center in a DC blocking scenario provided by an embodiment of the present application. As Figure 6 shown, the device is applied to the AC-DC tie-line parallel system, and 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 two-machine system. The device includes:

[0068] A physical model construction module 610, configured to establish a physical model of the AC-DC tie-line parallel system;

[0069] A mathematical model construction module 620 is configured to establish a mathematical model equivalent to the external characteristics of DC power transmission. The mathematical model characterizes the correlation between the DC equivalent parallel resistors connected to both sides of the AC bus, the DC active power, and the rated voltage of the bus.

[0070] A processing module 630 is configured to equivalently simplify the physical model according to the mathematical model to obtain an equivalent physical model of the AC-DC tie line parallel system, and calculate the equivalent electromotive forces on both sides of the DC power transmission according to the equivalent physical model.

[0071] An analysis module 640 is configured to calculate the ratio of the amplitudes of the equivalent electromotive forces according to the equivalent electromotive forces on both sides of the DC power transmission. When the AC-DC tie line parallel system is in a DC non-blocking scenario, substitute the ratio of the amplitudes of the equivalent electromotive forces into the oscillation center position function to analyze the oscillation center of the AC-DC tie line parallel system in the DC non-blocking scenario.

[0072] It can be seen that an analysis device for the oscillation center in a DC blocking scenario provided by an embodiment of the present application and the Figure 1 shown analysis method for the oscillation center in a DC blocking scenario are technical solutions based on the same inventive concept. Through the detailed description of the analysis method for the oscillation center in a DC blocking scenario provided by the above embodiment, those skilled in the art can clearly understand the implementation process of the analysis device for the oscillation center in a DC blocking scenario in this embodiment. Therefore, for the sake of simplicity of the specification, it will not be elaborated here.

[0073] Correspondingly, a multi-point pipeline regulation device under UHV DC interference provided by an embodiment of the present application first considers an equivalent two-machine system with AC-DC parallel connection as the architecture, takes the DC operating characteristics as the entry point, establishes a mathematical model, equivalently simplifies the physical model in combination with the mathematical model to obtain an equivalent physical model of the AC-DC tie line parallel system, thereby equivalently representing the external characteristics of the DC tie line as a dynamically changing impedance, and then calculates the equivalent electromotive forces on both sides of the DC power transmission according to the equivalent physical model, calculates the ratio of the amplitudes of the equivalent electromotive forces according to the equivalent electromotive forces on both sides of the DC power transmission. When the AC-DC tie line parallel system is in a DC non-blocking scenario, substitute the ratio of the amplitudes of the equivalent electromotive forces into the oscillation center position function to analyze the oscillation center of the AC-DC tie line parallel system in the DC non-blocking scenario.

[0074] In some embodiments, the expression of the mathematical model is: where P ref is the DC active power, r N is the DC equivalent parallel resistor connected to the N side of the AC bus, r M is the DC equivalent parallel resistor connected to the M side of the AC bus, is the square of the rated voltage of the bus.

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

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

[0077] Through circuit series-parallel transformation, equivalently transform the parallel resistor, the impedances on both sides of the AC bus, and the power source to obtain an equivalent physical model of the AC-DC tie line parallel system.

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

[0079]

[0080] Wherein, are respectively the equivalent coefficients after adding DC transmission, and are respectively the terminal voltages of the equivalent electromotive forces of the synchronous generators on both sides of the AC bus, r N is the DC equivalent parallel resistor connected to the N side of the AC bus, r M is the DC equivalent parallel resistor connected to the M side of the AC bus.

[0081] The specific embodiments described above further elaborate on the purpose, technical solution, and beneficial effects of the present application. It should be understood that the above description is only the specific embodiments of the present application and is not used to limit the protection scope of the present application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present application shall be included in the protection scope 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, which is formed by paralleling a single AC tie line with a DC transmission line in an equivalent two-machine system. The method includes: Establishing a physical model of the AC-DC tie line parallel system; Establishing a mathematical model equivalent to the external characteristics of DC transmission, where the mathematical model characterizes the relationship between the DC equivalent parallel resistance connected to both sides of the AC bus, the DC 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 the equivalent electromotive forces on both sides of the DC transmission according to the equivalent physical model. Among them, equivalently simplifying the physical model according to the mathematical model to obtain an equivalent physical model of the AC-DC tie line parallel system includes: according to the mathematical model, equivalently transforming the external characteristics of the DC transmission part of the physical model into a parallel resistance; through circuit series-parallel transformation, equivalently transforming the parallel resistance, the impedances on both sides of the AC bus, and the power source to obtain an equivalent physical model of the AC-DC tie line parallel system; Calculating the equivalent electromotive force amplitude ratio according to the equivalent electromotive forces on both sides of the DC transmission, and substituting the equivalent electromotive force amplitude ratio into the oscillation center position function when the AC-DC tie line parallel system is in the DC non-blocking scenario to analyze the oscillation center of the AC-DC tie line parallel system in the DC non-blocking scenario.

2. The method according to claim 1, wherein The expression of the mathematical model is 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 M side of the AC bus, is the square of the rated voltage of the bus.

3. The method according to claim 1, wherein The calculation formula for the equivalent electromotive forces on both sides of the DC transmission is: Among them, are respectively the equivalent coefficients after adding HVDC transmission, and are respectively the terminal voltages of the equivalent electromotive forces of the synchronous generators 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 is the DC equivalent parallel resistance connected to the M side of the AC bus.

4. The method according to claim 1, characterized in that, The expression of the oscillation center position function is: where δ is the phase angle difference of the synchronous voltages on both sides of the AC bus, and k e is the ratio of the equivalent potential amplitudes.

5. The method according to claim 1, characterized in that, The method further includes: When the AC-DC tie line parallel system is in the DC blocking scenario, substituting the ratio of the terminal voltages of the equivalent electromotive forces of the synchronous generators on both sides of the AC bus into the oscillation center position function to analyze the oscillation center of the AC-DC tie line parallel system in the DC blocking scenario.

6. An oscillation center analysis device in a DC blocking scenario, characterized in that, The device is applied to an AC-DC tie line parallel system, which is formed by paralleling a single AC tie line with a DC transmission line in an equivalent two-machine system. The device includes: A physical model construction module for establishing a physical model of the AC-DC tie line parallel system; A mathematical model construction module for establishing a mathematical model equivalent to the external characteristics of DC transmission, where the mathematical model characterizes the relationship between the DC equivalent parallel resistance connected to both sides of the AC bus, the DC active power, and the rated voltage of the bus; A processing module for 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 the equivalent electromotive forces on both sides of the DC transmission according to the equivalent physical model. Among them, the processing module is specifically used for: according to the mathematical model, equivalently transforming the external characteristics of the DC transmission part of the physical model into a parallel resistance; through circuit series-parallel transformation, equivalently transforming the parallel resistance, the impedances on both sides of the AC bus, and the power source to obtain an equivalent physical model of the AC-DC tie line parallel system; An analysis module for calculating the equivalent electromotive force amplitude ratio according to the equivalent electromotive forces on both sides of the DC transmission, and substituting the equivalent electromotive force amplitude ratio into the oscillation center position function when the AC-DC tie line parallel system is in the DC non-blocking scenario to analyze the oscillation center of the AC-DC tie line parallel system in the DC non-blocking scenario.

7. The device according to claim 6, characterized in that, The expression of the mathematical model is 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 M side of the AC bus, is the square of the rated voltage of the bus.

8. The device according to claim 6, characterized in that, The calculation formula for the equivalent electromotive forces on both sides of the DC power transmission is as follows: Among them, are respectively the equivalent coefficients after adding HVDC transmission, and are respectively the terminal voltages of the equivalent electromotive forces of the synchronous generators on both sides of the AC bus, r N is the DC equivalent shunt resistance connected to the N side of the AC bus, r M is the DC equivalent shunt resistance connected to the M side of the AC bus.

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