Method and device for analyzing power frequency oscillation characteristics of direct-current power transmission system

Abstract

The invention provides a power frequency oscillation characteristic analysis method and device of a direct current power transmission system, and belongs to the technical field of power grids. The method comprises the following steps: acquiring operation parameters of a direct-current power transmission system; establishing a sending end two-port network and a receiving end two-port network according to the operation parameters of the direct current power transmission system; establishing a direct current power transmission system circuit model based on the sending end two-port network and the receiving end two-port network; determining a transfer function of the DC power transmission system according to the DC power transmission system circuit model; and analyzing the power frequency oscillation characteristics of the DC power transmission system according to the transfer function. A two-port network of a sending end and a receiving end is established, the torque-frequency characteristic of the system is analyzed by applying a circuit principle, and the method can be suitable for low-frequency dynamic analysis, so that effective measures are taken to suppress power frequency oscillation.

Description

Technical Field

[0001] The present invention relates to the technical field of power grids, and in particular, to a method and device for analyzing the power-frequency oscillation characteristics of a DC transmission system. Background Art

[0002] With the growth of energy demand and the rapid development of new energy, the construction of a new power system has entered a critical period, and the global energy structure and power system structure are facing huge changes. Large-scale cross-regional consumption of clean energy is a major national demand. Research and development of high-voltage DC transmission technology with friendly new energy access characteristics and stronger system support capabilities to achieve reliable transmission of large-capacity clean energy over long distances is still one of the key issues to be solved. China's DC transmission technology has played an important role in the large-scale optimal allocation of energy resources, continuously improving the transmission capacity and grid-connected voltage, and achieving continuous innovation and breakthroughs in key technologies such as hierarchical access and cascade mixing. In a DC transmission system, due to the presence of voltage source converters, the system is prone to wide-frequency oscillation phenomena during various disturbances.

[0003] In the prior art, impedance analysis methods are usually used to model and guide the design of control strategies to suppress wide-frequency oscillations, enhance the stability and anti-interference ability of the system, and thus ensure the safe and stable operation of the power system. However, impedance analysis methods cannot be directly used for low-frequency dynamic analysis of power systems and cannot effectively avoid the occurrence of wide-frequency oscillations. Summary of the Invention

[0004] Embodiments of the present invention provide a method and device for analyzing the power-frequency oscillation characteristics of a DC transmission system to solve the problem that impedance analysis methods in the prior art are not applicable to low-frequency dynamic analysis and cannot effectively suppress the occurrence of wide-frequency oscillations.

[0005] In a first aspect, embodiments of the present invention provide a method for analyzing the power-frequency oscillation characteristics of a DC transmission system, including:

[0006] Obtaining the operating parameters of the DC transmission system;

[0007] Establishing a sending-end two-port network and a receiving-end two-port network according to the operating parameters of the DC transmission system;

[0008] Establishing a circuit model of the DC transmission system based on the sending-end two-port network and the receiving-end two-port network;

[0009] Determining the transfer function of the DC transmission system according to the circuit model of the DC transmission system;

[0010] Analyzing the power-frequency oscillation characteristics of the DC transmission system according to the transfer function.

[0011] In a second aspect, embodiments of the present invention provide a device for analyzing the power-frequency oscillation characteristics of a DC transmission system, including:

[0012] A parameter acquisition module, configured to acquire the operation parameters of a HVDC transmission system;

[0013] A first model establishment module, configured to establish a sending-end two-port network and a receiving-end two-port network according to the operation parameters of the HVDC transmission system;

[0014] A second model establishment module, configured to establish a circuit model of the HVDC transmission system based on the sending-end two-port network and the receiving-end two-port network;

[0015] A transfer function output module, configured to determine the transfer function of the HVDC transmission system according to the circuit model of the HVDC transmission system;

[0016] A characteristic analysis module, configured to analyze the power-frequency oscillation characteristics of the HVDC transmission system according to the transfer function

[0017] An embodiment of the present invention provides a method and device for analyzing the power-frequency oscillation characteristics of a HVDC transmission system. The method for analyzing the power-frequency oscillation characteristics of the HVDC transmission system includes: acquiring the operation parameters of the HVDC transmission system; establishing a sending-end two-port network and a receiving-end two-port network according to the operation parameters of the HVDC transmission system; establishing a circuit model of the HVDC transmission system based on the sending-end two-port network and the receiving-end two-port network; determining the transfer function of the HVDC transmission system according to the circuit model of the HVDC transmission system; analyzing the power-frequency oscillation characteristics of the HVDC transmission system according to the transfer function. In the embodiment of the present invention, two-port networks at the sending end and the receiving end are established, and the torque-frequency characteristics of the system are analyzed by using circuit principles, which can be applied to low-frequency dynamic analysis, so as to take effective measures to suppress power-frequency oscillation. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following will briefly introduce the drawings required for use in the embodiments or the description of the prior art. Obviously, the following drawings are only some embodiments of the present invention, and for those of ordinary skill in the art, other drawings can be obtained according to these drawings without creative efforts.

[0019] Figure 1 is a flowchart of the implementation of a method for analyzing the power-frequency oscillation characteristics of a HVDC transmission system provided by an embodiment of the present invention;

[0020] Figure 2 is a block diagram of a single-port model of a synchronous machine provided by an embodiment of the present invention;

[0021] Figure 3 is a single-port equivalent circuit diagram of a synchronous machine provided by an embodiment of the present invention;

[0022] Figure 4It is the block diagram of the VSC small-signal model provided by the embodiment of the present invention;

[0023] Figure 5 It is the block diagram of the models of various links of the VSC and the circuit model provided by the embodiment of the present invention;

[0024] Figure 6 It is the single-port circuit model of the VSC provided by the embodiment of the present invention;

[0025] Figure 7 It is the two-port network model provided by the embodiment of the present invention;

[0026] Figure 8 It is the circuit model of the DC transmission system provided by the embodiment of the present invention;

[0027] Figure 9 It is the structural schematic diagram of the device for analyzing the power-frequency oscillation characteristics of the DC transmission system provided by the embodiment of the present invention. Detailed implementation manners

[0028] In the following description, for the purpose of illustration rather than limitation, specific details such as specific system structures and technologies are presented to thoroughly understand the embodiments of the present invention. However, those skilled in the art should clearly understand that the present invention can also be implemented in other embodiments without these specific details. In other cases, detailed descriptions of well-known systems, devices, circuits, and methods are omitted to avoid unnecessary details from interfering with the description of the present invention.

[0029] To make the purpose, technical solutions, and advantages of the present invention clearer, the following will be described through specific embodiments with reference to the accompanying drawings.

[0030] Figure 1 It is the implementation flowchart of a method for analyzing the power-frequency oscillation characteristics of a DC transmission system provided by the embodiment of the present invention, which is described in detail as follows:

[0031] The above method for analyzing the power-frequency oscillation characteristics of the DC transmission system includes:

[0032] S101: Obtain the operating parameters of the DC transmission system;

[0033] S102: Establish a sending-end two-port network and a receiving-end two-port network according to the operating parameters of the DC transmission system;

[0034] A DC transmission system is a power transmission system that converts alternating current into direct current through a converter station, transmits it through a DC transmission line, and then converts the direct current into alternating current at another converter station.

[0035] The DC power transmission system includes: a synchronous machine (SG), a sending-end voltage source converter (sending-end VSC), and a receiving-end voltage source converter (receiving-end VSC). At the sending-end VSC, alternating current is converted into direct current through a rectifier; the rectified direct current is transmitted through a DC power transmission line; at the receiving-end VSC, the direct current is converted back into alternating current through an inverter. Compared with the traditional AC power transmission system, it has unique advantages, especially in applications such as long-distance, large-capacity power transmission and asynchronous networking.

[0036] In the embodiment of the present invention, based on the generalized circuit modeling method using torque-frequency dynamic analysis, a two-port network at the sending end and a two-port network at the receiving end are established to form a circuit model of the DC power transmission system for circuit analysis.

[0037] In a possible implementation manner, S102 may include:

[0038] S1021: Establish a single-port model of the synchronous machine according to the operating parameters of the DC power transmission system;

[0039] Power system stability is a complex issue. Rotor angle stability includes synchronous stability, frequency stability, and voltage stability. Rotor angle stability refers to the ability of interconnected generator sets to maintain synchronization, which is classified as a short-term phenomenon involving electromechanical oscillations in the power system. Different from frequency stability that depends on the balance of power generation and load in the medium and long term, rotor angle stability is mainly related to inertia and damping, which is a dynamic concept in the short term. Although small-signal stability analysis is based on a linearization method, in most practical cases, this method is also effective for nonlinear dynamic responses. Since its analysis results only depend on the initial state of the system, it is applicable to modern power systems with various small disturbances.

[0040] To study the stability of the rotor angle, a suitable small-signal model needs to be established. On the one hand, it is complex to establish an accurate model to describe the complete dynamics of the synchronous machine. It is a seventh-order mathematical model composed of two parts: a second-order mechanical model and a fifth-order electrical model. Although the accurate model has certain theoretical research value, the order of the overly accurate model is relatively high, it is more complex, difficult to analyze, and has limited practicality. Therefore, according to dynamics and different accuracy requirements, simplified reduced-order models of the synchronous machine have been widely used in practical applications. In terms of rotor angle stability, the transients and subtransients of electromechanical dynamics can be ignored. On the other hand, some auxiliary components in the synchronous machine can also be ignored in the analysis of rotor angle stability.

[0041] For a power system based on SG (for example, the DC power transmission system provided in the embodiment of the present invention), inertia characteristics, synchronization ability, and electromechanical oscillation damping are key characteristics affecting rotor angle stability.

[0042] In a possible implementation manner, the embodiments of the present invention can be described by using the classical Phillips-Heffron model. The Phillips-Heffron model can clearly and intuitively reflect the small-signal dynamic relationship between the rotor angle and the angular frequency, and is an effective tool for stability analysis and control.

[0043] Specifically, the single-port model of the synchronous machine may include:

[0044]

[0045] Wherein, K J is the equivalent inertia coefficient, K S is the synchronizing coefficient, K D is the damping coefficient; T in is the input torque, δ is the rotor angle, and ω is the rotor angular frequency.

[0046] Figure 2 And Figure 3 shows the block diagram and equivalent circuit diagram of the single-port model of the synchronous machine. The single-port model of the synchronous machine provided by the embodiments of the present invention only includes AC variables, torque, and angular frequency.

[0047] S1022: Establish a single-port model of the sending-end VSC according to the operating parameters of the DC transmission system;

[0048] Figure 4 shows the small-signal model block diagram of the VSC. The model block diagram is the main basis for converting to the circuit model, and the model block diagrams and circuit models of each link have the same mathematical model.

[0049] The small-signal model block diagram of the VSC mainly includes the VI curve slope, DC capacitor, and AC frequency-DC voltage control link. The VI curve slope link can be analogized to a resistor element, and the AC frequency-DC voltage control link can be analogized to an ideal transformer. The converted model block diagrams and circuit models of each link refer to Figure 5 . The feedback network is divided into two basic types: nodes and loops. Among them, the voltage adder corresponds to the loop and is analogized to resistor series voltage division; the current adder can be characterized by a node where multiple branches converge and is analogized to current shunt. The model block diagrams and circuit models of voltage and current algebraic operations refer to Figure 5 .

[0050] According to the above principles, the single-port circuit model of the VSC (the single-port model of the sending-end VSC) can be obtained. The specific circuit structure of the single-port circuit model of the VSC can refer to Figure 6 , and will not be elaborated here specifically. There are only two variables, voltage and current, in the model.

[0051] Furthermore, the single-port model of the receiving-end VSC can be obtained by using the same method.

[0052] S1023: Obtain the sending-end two-port network according to the single-port model of the synchronous machine and the single-port model of the sending-end VSC.

[0053] For the sending-end VSC and the receiving-end VSC that actively participate in frequency regulation, since the DC-side voltage is strongly correlated with the AC frequency, when modeling, it is necessary to consider not only the frequency response of the AC interface but also the voltage dynamics of the DC interface. Based on the idea of the unified energy path and the energy hub, construct the hub model of the AC-DC hybrid system - the VSC two-port network (for example, the sending-end two-port network). There is a conversion of electrical energy in AC and DC forms in the VSC. According to the concept of the energy hub, it can be abstracted into a linearized two-port circuit model. Among them, the variables of the AC port are T - ω instead of u abc and i abc , and the variables of the DC port are consistent with the actual situation, as shown in Table 1.

[0054] Table 1 AC and DC port parameter table

[0055]

[0056] At this time, the simplification conditions that the modeling should meet: ignore the VSC loss and ignore the resistance component of the transmission line in the AC system. This condition satisfies the non-energy characteristics and is the basis for constructing the core part of the two-port circuit model - the ideal transformer.

[0057] The VSC single-port circuit model can only describe the self-dynamics of the VSC and cannot depict the dynamic relationship between the AC and DC sides. Therefore, it is necessary to expand the VSC single-port circuit model into a two-port circuit model. The AC port variables use active power - frequency, and the DC port variables use DC voltage - current. The AC and DC sides can try to be coupled through an ideal transformer. However, in practice, the variables on the AC side and the DC side cannot be directly matched with the turns ratio of the transformer. The key to establishing the two-port circuit model lies in how to construct an ideal transformer model to couple the dynamics of the DC voltage and the AC frequency.

[0058] Under the small disturbance condition at the steady-state operating point, the sending-end VSC and the receiving-end VSC satisfy the power equation:

[0059] U DCN ΔI hv = ω s ΔT hv

[0060] Among them, ω s is the rated angular frequency, U DCN is the DC voltage reference value, ΔI hv is the current disturbance of the VSC single-port model, and ΔT hvis the torque variation.

[0061] Based on the above formula and the frequency modulation link of the sending-end VSC, we can get:

[0062]

[0063] Due to N DC ≠1, in order to use ideal transformer components to describe the torque-frequency dynamic relationship of VSC

[0064] System, let ΔI mhv =N DC ΔI hv and ΔU mDC =ΔU DC Substituting the above formula, we can get:

[0065]

[0066] The above formula is consistent with the VCR of an ideal transformer element, and a two-port circuit model can be constructed based on it.

[0067] From the above, it can be seen that in a possible implementation mode, reference Figure 7 , the two-port network at the sending end may include: equivalent capacitance on the DC side, equivalent transformer and equivalent inductance on the AC side;

[0068] A two-port network at the sending end, wherein the first AC end is connected to the first like-name end of the equivalent transformer through the AC side equivalent inductor, the second AC end is connected to the first opposite-name end of the equivalent transformer, the positive DC end is respectively connected to the first end of the DC side equivalent capacitor and the second like-name end of the equivalent transformer, and the negative DC end is connected to the second opposite-name end of the DC transformer.

[0069] In one possible implementation, reference Figure 8 , the circuit structure of the two-port network at the sending end can be the same as the circuit structure of the two-port network at the receiving end.

[0070] Considering ΔI hv to ΔI mhv The admittance also needs to be converted, Y mhv =N DC Y hv According to the equivalent inductance component L hv Parameters and synchronization coefficient K S Regarding the parameters of the AC filter inductor corresponding to the physical link, it is placed on the AC side in the two-port network at the sending end. Based on the above, we can get:

[0071]

[0072] That is, the formula of the two-port network at the sending end can include:

[0073]

[0074] Among them, L hvω1 is the equivalent inductance on the AC side, C mhv1 is the equivalent capacitance on the DC side, n hv1 is the turns ratio of the equivalent transformer, N DC is the coefficient that converts the deviation of the DC voltage into the change of the AC side frequency, ω s is the rated angular frequency, U DCN is the reference value of the DC voltage, K S is the synchronization coefficient.

[0075] Similarly, the receiving-end two-port network can be established by the same method, and the details are not described here.

[0076] As can be seen from the above, in the embodiment of the present invention, the Phillips–Heffron model equivalent to the VSC and SG is used to correspond the model block diagram to the circuit model one by one, and conversion is performed to obtain the sending-end VSC single-port model and the receiving-end VSC single-port model. At this time, there are only two variables in the model: voltage and current, and they are direct current quantities. Then, through variable conversion, an ideal transformer is designed to couple the direct current quantity and the alternating current quantity, calculate the turns ratio of the ideal transformer, construct the sending-end two-port network and the receiving-end two-port network, and further establish the circuit model of the DC transmission system.

[0077] S103: Establish the circuit model of the DC transmission system based on the sending-end two-port network and the receiving-end two-port network;

[0078] In a possible implementation manner, referring to Figure 8 , S103 may include:

[0079] S1031: Connect the DC side of the sending-end two-port network to the DC side of the receiving-end two-port network through a DC transmission line to obtain the circuit model of the DC transmission system;

[0080] Among them, the DC transmission line may include: equivalent resistance and equivalent inductance.

[0081] The sending-end VSC and the receiving-end VSC of the DC transmission system are connected through a transmission line. Ignoring the single-port models of the sending-end synchronous machine and the receiving-end synchronous machine, the circuit model of the DC transmission system can be obtained, referring to Figure 8 .

[0082] S104: Determine the transfer function of the DC transmission system according to the circuit model of the DC transmission system;

[0083] The transfer function is the ratio of the output variable (such as the receiving-end DC voltage, power, etc.) to the input variable (such as the sending-end DC voltage, trigger angle change, etc.) in the complex frequency domain, and it can clearly represent the dynamic response characteristics of the system.

[0084] Based on the above DC transmission system circuit model, the differential equations (obtained from Kirchhoff's laws and component characteristic equations) describing the dynamic process of the system are Laplace-transformed to convert the time-domain equations into complex-frequency-domain equations. During the Laplace transform process, using the initial conditions and the linear characteristics of the system, the system equations in the form of transfer functions are obtained.

[0085] S105: Analyze the power-frequency oscillation characteristics of the DC transmission system according to the transfer function.

[0086] In a possible implementation, S105 may include:

[0087] S1051: Determine the frequency, damping characteristics, and power-frequency stability of the power-frequency oscillation of the DC transmission system according to the transfer function.

[0088] In a possible implementation, S1051 may include:

[0089] 1. Determine the zeros and extreme points of the transfer function, and based on the zeros and extreme points of the transfer function, determine the frequency and damping characteristics of the power-frequency oscillation of the DC transmission system;

[0090] Through the distribution of the poles and zeros of the transfer function, the frequency and damping conditions of the power-frequency oscillation of the DC transmission system can be determined. The real part of the pole represents the damping of the oscillation, and the imaginary part represents the oscillation frequency. If the real part of the pole is negative, it indicates that the system is stable, and the greater the damping, the faster the oscillation of the system decays; if the real part is positive, the system is unstable, and the power-frequency oscillation will continuously increase.

[0091] 2. Determine the power-frequency stability of the DC transmission system according to the Routh-Hurwitz criterion.

[0092] The Routh-Hurwitz criterion is an algebraic criterion for judging the stability of a linear time-invariant system based on the coefficients of the system characteristic equation. The necessary and sufficient condition for the system to be stable is that all roots have negative real parts. The Routh-Hurwitz criterion transforms this condition into a series of inequality constraints on the coefficients of the characteristic equation. Its core idea is to construct a Routh array through specific mathematical operations on the coefficients, and then observe the signs of the elements in the array to judge whether the system is stable.

[0093] In the embodiments of the present invention, the stability of the HVDC transmission system can be determined according to the Routh-Hurwitz criterion. If the judgment result is unstable, the system needs to be optimized. The optimization measures may include adjusting the control parameters of the HVDC transmission system (such as the trigger angle and extinction angle of the converter), changing the system structure (such as adding or adjusting components such as filters and reactors), or improving the control strategy (such as adopting a new controller design method), etc., to ensure the stability of the system and improve the reliable operation ability of the HVDC transmission system under various working conditions.

[0094] Meanwhile, the relationship between the input variable and the output variable in the transfer function can also be analyzed. For example, when the frequency of the sending-end AC system changes, the changes in the receiving-end DC voltage and power can be calculated through the transfer function, so as to understand the response characteristics of the HVDC transmission system to the frequency disturbance of the AC system and how this response affects the power-frequency stability of the system.

[0095] It should be understood that the magnitudes of the sequence numbers of the steps in the above embodiments do not mean the order of execution. The execution order of each process should be determined according to its function and internal logic, and should not constitute any limitation to the implementation process of the embodiments of the present invention.

[0096] The following are the device embodiments of the present invention. For the details not described in detail, reference can be made to the corresponding method embodiments above.

[0097] Figure 9 The structural schematic diagram of a device for analyzing the power-frequency oscillation characteristics of an HVDC transmission system provided by an embodiment of the present invention is shown. For the convenience of description, only the parts related to the embodiments of the present invention are shown and are described in detail as follows:

[0098] As Figure 9 shown, the device for analyzing the power-frequency oscillation characteristics of an HVDC transmission system may include:

[0099] A parameter acquisition module 21, configured to acquire the operation parameters of the HVDC transmission system;

[0100] A first model establishment module 22, configured to establish a sending-end two-port network and a receiving-end two-port network according to the operation parameters of the HVDC transmission system;

[0101] A second model establishment module 23, configured to establish an HVDC transmission system circuit model based on the sending-end two-port network and the receiving-end two-port network;

[0102] A transfer function output module 24, configured to determine the transfer function of the HVDC transmission system according to the HVDC transmission system circuit model;

[0103] A characteristic analysis module 25, configured to analyze the power-frequency oscillation characteristics of the HVDC transmission system according to the transfer function.

[0104] In a possible implementation manner, the first model establishment module 22 may include:

[0105] A synchronous machine model establishment unit, configured to establish a single-port model of the synchronous machine according to the operation parameters of the DC power transmission system;

[0106] A single-port model establishment unit, configured to establish a single-port model of the sending-end VSC according to the operation parameters of the DC power transmission system;

[0107] A two-port model establishment unit, configured to obtain a sending-end two-port network according to the single-port model of the synchronous machine and the single-port model of the sending-end VSC.

[0108] In a possible implementation manner, the sending-end two-port network may include: a DC-side equivalent capacitor, an equivalent transformer, and an AC-side equivalent inductor;

[0109] For the sending-end two-port network, the first AC end is connected to the first homonymous end of the equivalent transformer through the AC-side equivalent inductor, the second AC end is connected to the first non-homonymous end of the equivalent transformer, the positive DC end is respectively connected to the first end of the DC-side equivalent capacitor and the second homonymous end of the equivalent transformer, and the negative DC end is connected to the second non-homonymous end of the DC transformer.

[0110] In a possible implementation manner, the formula of the sending-end two-port network may include:

[0111]

[0112] Wherein, L hvω1 is the AC-side equivalent inductor, C mhv1 is the DC-side equivalent capacitor, n hv1 is the turns ratio of the equivalent transformer, N DC is the change coefficient for converting the deviation of the DC voltage into the change of the AC-side frequency, ω s is the rated angular frequency, U DCN is the DC voltage reference value, and K S is the synchronization coefficient.

[0113] In a possible implementation manner, the single-port model of the synchronous machine may include:

[0114]

[0115] Wherein, K J is the equivalent inertia coefficient, K S is the synchronization coefficient, K D is the damping coefficient; T in is the input torque, δ is the rotor angle, and ω is the rotor angular frequency.

[0116] In a possible implementation, the circuit structure of the sending-end two-port network may be the same as that of the receiving-end two-port network.

[0117] In a possible implementation, the second model establishment module 23 may specifically be used for: connecting the DC side of the sending-end two-port network to the DC side of the receiving-end two-port network through a DC transmission line to obtain a circuit model of the DC transmission system;

[0118] Wherein, the DC transmission line may include: an equivalent resistance and an equivalent inductance.

[0119] In a possible implementation, the characteristic analysis module 25 may specifically be used for: determining the frequency, damping characteristic, and power-frequency stability of the power-frequency oscillation of the DC transmission system according to the transfer function.

[0120] In a possible implementation, determining the frequency, damping characteristic, and power-frequency stability of the power-frequency oscillation of the DC transmission system according to the transfer function may include:

[0121] 1. Determining the zeros and extreme points of the transfer function, and determining the frequency and damping characteristic of the power-frequency oscillation of the DC transmission system according to the zeros and extreme points of the transfer function;

[0122] 2. Determining the power-frequency stability of the DC transmission system according to the Routh-Hurwitz criterion.

[0123] In the above embodiments, the descriptions of the respective embodiments have their own emphases. For parts not detailed or recorded in a certain embodiment, reference may be made to the relevant descriptions of other embodiments.

[0124] Those of ordinary skill in the art can realize that the templates, units, and algorithm steps of the examples described in combination with the embodiments disclosed herein can be implemented by electronic hardware, or by a combination of computer software and electronic hardware. Whether these functions are executed in a hardware or software manner depends on the specific application and design constraints of the technical solution. Skilled professionals can use different methods to implement the described functions for each specific application, but such implementation should not be considered to exceed the scope of the present invention.

[0125] If a module / unit is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, to implement all or part of the processes in the above-described embodiment methods of the present invention, it can also be completed by a computer program instructing related hardware. The computer program can be stored in a computer-readable storage medium. When the computer program is executed by a processor, the steps of the above-described embodiments of the power-frequency oscillation characteristic analysis method for each DC transmission system can be implemented. Among them, the computer program includes computer program code, and the computer program code can be in the form of source code, object code, executable file, or some intermediate form, etc. The computer-readable medium can include: any entity or device capable of carrying computer program code, recording medium, USB flash drive, mobile hard disk, magnetic disk, optical disc, computer memory, read-only memory, random access memory, electrical carrier signal, telecommunication signal, and software distribution medium, etc.

[0126] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements for some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the various embodiments of the present invention, and should all be included in the protection scope of the present invention.

Claims

1. A method for analyzing power frequency oscillation characteristics of a direct current transmission system, characterized in that: include: Obtaining operating parameters of the DC transmission system; Establishing a sending-end two-port network and a receiving-end two-port network according to the operating parameters of the DC transmission system; Establishing a DC power transmission system circuit model based on the sending-end two-port network and the receiving-end two-port network; Determining a transfer function of the DC power transmission system according to the DC power transmission system circuit model; The power frequency oscillation characteristics of the direct current power transmission system are analyzed according to the transfer function.

2. The method for analyzing power frequency oscillation characteristics of a direct current transmission system according to claim 1, characterized in that: The step of establishing a sending-end two-port network according to the operating parameters of the DC power transmission system comprises: Establishing a single-port model of a synchronous machine according to the operating parameters of the DC transmission system; Establishing a sending-end VSC single-port model according to the operating parameters of the DC transmission system; The sending-end two-port network is obtained according to the single-port model of the synchronous machine and the single-port model of the sending-end VSC.

3. The method for analyzing power frequency oscillation characteristics of a direct current transmission system according to claim 2, characterized in that: The sending-end two-port network includes: a DC side equivalent capacitor, an equivalent transformer and an AC side equivalent inductor; The sending-end two-port network has a first AC end connected to the first like-name end of the equivalent transformer through the AC-side equivalent inductor, a second AC end connected to the first opposite-name end of the equivalent transformer, a positive DC end connected to the first end of the DC-side equivalent capacitor and the second like-name end of the equivalent transformer, and a negative DC end connected to the second opposite-name end of the DC transformer.

4. The method for analyzing power frequency oscillation characteristics of a direct current transmission system according to claim 3, characterized in that: The formula of the sending-end two-port network includes: Among them, L hvω1 is the equivalent inductance on the AC side, C mhv1 is the DC side equivalent capacitance, n hv1 is the transformation ratio of the equivalent transformer, N DC is the coefficient of change of the DC voltage deviation into the AC side frequency, ω s is the rated angular frequency, U DCN is the DC voltage reference value, K S is the synchronization coefficient.

5. The method for analyzing power frequency oscillation characteristics of a direct current transmission system according to claim 4, characterized in that: The single-port model of the synchronous machine includes: Among them, K J is the equivalent inertia coefficient, K S is the synchronization coefficient, K D is the damping coefficient; T in is the input torque, δ is the rotor angle, and ω is the rotor angular frequency.

6. The method for analyzing power frequency oscillation characteristics of a direct current transmission system according to claim 4, characterized in that: The circuit structure of the sending-end two-port network is the same as the circuit structure of the receiving-end two-port network.

7. The method for analyzing power frequency oscillation characteristics of a direct current transmission system according to any one of claims 1 to 6, characterized in that: The establishing of a DC power transmission system circuit model based on the sending-end two-port network and the receiving-end two-port network includes: Connecting the DC side of the sending-end two-port network to the DC side of the receiving-end two-port network through a DC transmission line to obtain a circuit model of the DC transmission system; Wherein, the DC transmission line includes: equivalent resistance and equivalent inductance.

8. The method for analyzing power frequency oscillation characteristics of a direct current transmission system according to any one of claims 1 to 6, characterized in that: The analyzing the power frequency oscillation characteristics of the DC power transmission system according to the transfer function comprises: According to the transfer function, the frequency, damping characteristics and power frequency stability of the power frequency oscillation of the direct current power transmission system are determined.

9. The method for analyzing power frequency oscillation characteristics of a direct current transmission system according to claim 8, characterized in that: Determining the frequency, damping characteristics and power frequency stability of the power frequency oscillation of the DC power transmission system according to the transfer function includes: Determine the zero point and the extreme point of the transfer function, and determine the frequency and damping characteristics of the power frequency oscillation of the direct current power transmission system according to the zero point and the extreme point of the transfer function; The power-frequency stability of the DC power transmission system is determined according to the Routh-Hurwitz criterion.

10. A power frequency oscillation characteristic analysis device for a direct current transmission system, characterized in that: include: A parameter acquisition module, used to acquire operating parameters of the DC transmission system; A first model building module is used to build a sending-end two-port network and a receiving-end two-port network according to the operating parameters of the DC power transmission system; A second model building module is used to build a DC power transmission system circuit model based on the sending-end two-port network and the receiving-end two-port network; A transfer function output module, used for determining the transfer function of the DC power transmission system according to the DC power transmission system circuit model; The characteristic analysis module is used to analyze the power frequency oscillation characteristics of the direct current power transmission system according to the transfer function.

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