Stability Analysis And Controller Design Of VSC-HVDC Transmission System

With the innovation of power electronics technology and the demand of power grid development strategy implementation,the application of high-voltage DC transmission technology has been paid attention to VSC-HVDC technology can effectively absorb new energy with large fluctuations and poor stability,as well as the regenerative energy that fed in system.And It can reduce the space occupied by the transmission system and increase the transmission capacity of the transmission system.At the same time,it can be used to improve the power quality of the distribution network and improve the reliability of power supply,and better promote the development process of DC asynchronous interconnection of regional power grids in our country.Therefore,it is of great importance to carry out detailed research on the stability of VSC-HVDC transmission system and its corresponding controllers,which can provide certain theoretical support and design reference for engineering application and promotion.Firstly,a general small-signal model of a VSC-HVDC system is established.The versatility of the small-signal model built in this paper is reflected from the aspects of system topology and synchronous rotating coordinate system.The versatility of the system topology is reflected in the small signal model that it considers the various system components and control links in the system in detail.The versatility of the synchronous rotating coordinate system is reflected in that both the variability of the AC network and the fluctuation of the power frequency angular velocity of point of common coupling(PCC)voltage are considered when constructing it.It is proposed to construct this synchronous rotating coordinate system based on the equivalent voltage source voltage.Secondly,according to the above theoretical analysis,the corresponding small-signal model is built based on MATLAB / Simulink.When the active power of the converter station 1 is disturbed,the current and voltage on both sides of the system will also fluctuate.In this case,the correctness of the small-signal model of the system is verified by comparing and analyzing the simulated waveform of the small signal model with the simulation waveform of the electromagnetic transient model in PSCAD / EMTDC.Then,integrated modal analysis method,the participation factor analysis method and the sensitivity analysis method to summarize a set of stability analysis methods and steps for the linear small-signal model.Two cases are used to prove the application of the stability analysis method in identifying the source of system instability and improving the stability of THE system.At the same time,some relevant control parameters affecting the stability of the VSCHVDC system are found out,and the stability domain of the corresponding parameters is determined.Finally,based on the Lyapunov stability theory,the stabilizing switching law of the bidirectional converter is derived,which makes the system energy attenuate fastest,and the stabilizing switching controller is designed according to the switching law.Then the effectiveness of the controller is verified by simulation,and the superiority of the stabilizing switching control strategy is proved from the theoretical and simulation aspects by comparison with the traditional current vector control strategy.