CN-121981027-A - VSC-HVDC direct-current capacitor design method considering load uncertainty

CN121981027ACN 121981027 ACN121981027 ACN 121981027ACN-121981027-A

Abstract

The invention relates to the technical field of power electronics and direct current transmission, in particular to a VSC-HVDC direct current capacitor design method considering load uncertainty, which comprises the following steps: step one, a state space model is established; establishing a model containing uncertain variables; step three, a stability criterion; and fourthly, the DC capacitor algorithm design realizes the expansion of the DC capacitor design from a fixed operating point to a load change interval by introducing load uncertainty modeling, constructing a computable robust stability criterion and combining a systematic parameter searching method, has obvious advantages in the aspects of applicability, calculation feasibility and engineering guidance significance compared with the prior art, and realizes the expansion of the DC capacitor design from the fixed operating point to the load change interval by introducing load uncertainty modeling, constructing the computable robust stability criterion and combining the systematic parameter searching method.

Inventors

LIU JIANZHE
LI CANBING
SHI ZICAI
LI FENG
WANG YANFENG
PENG SUI

Assignees

上海交通大学

Dates

Publication Date: 20260505
Application Date: 20260319

Claims (7)

1. A method for designing a VSC-HVDC direct current capacitor by considering load uncertainty comprises a first step of establishing a state space model, a second step of establishing a model containing uncertain variables, a third step of determining stability criteria, a fourth step of designing a direct current capacitor algorithm, and is characterized in that: in the first step, a state space model of the VSC-HVDC system is firstly established; In the second step, a linearization state space model of the VSC-HVDC system containing uncertain variables is established; in the third step, a robust stability criterion is established based on a robust optimization theory; In the fourth step, a dc capacitance design method is constructed based on the dichotomy.
2. The method for designing the VSC-HVDC DC capacitor taking load uncertainty into consideration according to claim 1, wherein in the first step, the method for establishing the state space model comprises the following steps: S1, defining a reference direction, and establishing a mathematical model of a two-end two-level VSC-HVDC system main circuit, wherein the main circuit comprises a transmitting end, a direct current side and a receiving end, and the main circuit model comprises an alternating current side, a direct current side and an alternating current-direct current connection; s2, establishing a state space model of a VSC-HVDC system converter station control system according to a control structure diagram, wherein the station control system comprises a transmitting end and a receiving end converter station control system; S3, defining a state variable vector and an input variable vector, synthesizing the state equations of the models, and jointly forming a state equation set by a plurality of state equations to obtain a state space model of the VSC-HVDC system.
3. The VSC-HVDC direct current capacitor design method considering load uncertainty according to claim 2 is characterized in that for the alternating current side model, a circuit equation set under a three-phase static coordinate system is established based on kirchhoff law, park conversion is used for converting the circuit equation set into a synchronous rotation coordinate system, for the direct current side, the circuit equation set established by using kirchhoff law is a required model, and for an alternating current and direct current connection model, an alternating current and direct current connection equation is established by using energy conservation law.
4. The method for designing the VSC-HVDC direct current capacitor taking load uncertainty into consideration according to claim 2, wherein the station control system comprises a transmitting end and a receiving end converter station control system, and the basic controller adopted by the control system is a PI controller in the selection of state variables.
5. The method for designing the VSC-HVDC DC capacitor taking load uncertainty into consideration according to claim 2, wherein in the second step, the method comprises the following steps: s1, carrying out Taylor series expansion on a polynomial in the state equation set, reserving a primary term, and establishing a small signal model; S2, screening the jacobian matrix in the small signal model to obtain an uncertain variable, wherein the uncertain variable is formed by combining a parameter showing the size of a load and a steady state value of a state variable having an influence on the size of an element of the jacobian matrix, and the linearization state space model of the system is expressed into the jacobian matrix form containing linear uncertain variables.
6. The method for designing the VSC-HVDC DC capacitor taking load uncertainty into consideration as set forth in claim 1, wherein in the third step, the construction method comprises the following steps: S1, defining the upper and lower bounds of a variation interval of uncertain parameters in a jacobian matrix so as to obtain the upper and lower bounds of the variation interval of an uncertain variable formed by combining the uncertain parameters, wherein when the uncertain variable varies in a non-empty set, there are countless different jacobian matrices, and according to a linear steady system Lyapunov theory, if one common Lyapunov matrix exists so that all the jacobian matrices meet respective Lyapunov inequality, all the jacobian matrices are Hurwitz stable, so that when a load varies in a given interval, the balance points of the corresponding VSC-HVDC system are locally asymptotically stable and are called robust stable; S2, because the robust stability criterion containing countless LMI constraints is actually an uncertain semi-definite programming problem and the constraint of an uncertain variable is an interval constraint, the criterion can be equivalently converted into a criterion which has a limited number of LMI constraints and is irrelevant to the number of uncertain variables, and particularly a robust stability criterion containing two LMI constraints.
7. The method of designing a direct current capacitor of VSC-HVDC with load uncertainty as claimed in claim 6, wherein in the fourth step, the direct current capacitor parameter is designed to obtain a smaller value meeting stability requirement, and the parameter is embodied in the robust stability criterion, the algorithm of constructing-designing the direct current capacitor is constructed by using dichotomy logic, the algorithm comprises an algorithm starting from any selected capacitance interval as long as the interval contains any capacitance value enabling the criterion containing two LMI constraints to be met, then substituting the midpoint of the capacitance interval into the criterion, if the criterion is met, updating the upper boundary of the capacitance interval to be the midpoint, otherwise updating the lower boundary of the capacitance interval to be the midpoint, thereby obtaining a new capacitance interval which is reduced, and randomly selecting a capacitance interval as long as the interval contains an initial guess value enabling the problem to be solved, then solving the problem at the midpoint of the interval, if the solution is met, replacing the upper boundary of the current interval with the midpoint, and repeating the capacitance interval until the tolerance is met, namely the new capacitance interval is designed as the latest boundary.

Description

VSC-HVDC direct-current capacitor design method considering load uncertainty Technical Field The invention belongs to the technical field of power electronics and direct current transmission, and particularly relates to a VSC-HVDC direct current capacitor design method considering load uncertainty. Background VSC-HVDC is a flexible direct current transmission, abbreviated as flexible direct current, commonly used for transmitting power from a remote power supply center to a load center, in such transmission systems, the variation of the transmission power affects the stability margin of the system, and the dc capacitor is a buffer device for suppressing power disturbances, and by proper design, for example, if the magnitude of the capacitance exceeds a certain threshold, the system can remain stable under given load conditions. The prior art has conducted a lot of researches about stability analysis of a VSC-HVDC system and selection of direct current capacitance parameters, but there are still a number of defects in quantitative design of the direct current capacitance, firstly, the existing stability analysis method generally assumes that an operation balance point of the system is fixed and known, and analyzes the stability of the system based on the balance point, however, in an actual power system, load power has uncertainty and time variability, and the actual operation balance point of the VSC-HVDC system is often difficult to accurately acquire in advance along with the change of load conditions. Under the above circumstances, the stability analysis result based on the fixed balance point assumption is difficult to be directly used for guiding the engineering design of the direct current capacitor, and secondly, although the influence rule of the direct current capacitor on the dynamic stability of the VSC-HVDC system is revealed from the analysis angle in the prior art, the related research stays at the analysis level, but a method capable of systematically and quantitatively selecting the direct current capacitor under the condition of uncertain load is not formed yet, especially in the application scenario that the system stability and engineering economy are simultaneously considered, how to reasonably determine the capacitance value of the direct current capacitor on the premise of meeting the stability requirement is still lacking in effective design basis and the technical scheme of the system. Disclosure of Invention The invention aims to solve the problems and provide the VSC-HVDC direct-current capacitor design method which is simple in structure and reasonable in design and takes load uncertainty into consideration. The invention realizes the above purpose through the following technical scheme: A design method of a VSC-HVDC direct current capacitor considering load uncertainty comprises the steps of establishing a state space model, establishing a model containing uncertain variables, establishing a stability criterion, and designing a direct current capacitor algorithm; in the first step, a state space model of the VSC-HVDC system is firstly established; In the second step, a linearization state space model of the VSC-HVDC system containing uncertain variables is established; in the third step, a robust stability criterion is established based on a robust optimization theory; In the fourth step, a dc capacitance design method is constructed based on the dichotomy. Preferably, in the first step, the method for establishing a state space model includes: S1, defining a reference direction, and establishing a mathematical model of a two-end two-level VSC-HVDC system main circuit, wherein the main circuit comprises a transmitting end, a direct current side and a receiving end, and the main circuit model comprises an alternating current side, a direct current side and an alternating current-direct current connection; s2, establishing a state space model of a VSC-HVDC system converter station control system according to a control structure diagram, wherein the station control system comprises a transmitting end and a receiving end converter station control system; S3, defining a state variable vector and an input variable vector, synthesizing the state equations of the models, and jointly forming a state equation set by a plurality of state equations to obtain a state space model of the VSC-HVDC system. Preferably, for the alternating current side model, a circuit equation set under a three-phase static coordinate system is established based on kirchhoff's law, park conversion is used for converting the circuit equation set to a synchronous rotation coordinate system, for the direct current side, the circuit equation set established by using kirchhoff's law is the required model, and for the alternating current and direct current connection model, an alternating current and direct current connection equation is established by using an energy conservation law. Preferably, the station control sy