Research On Modeling And Control Of HVDC Transmission System

With the vigorous development of new energy technologies such as wind power generation and photovoltaic power generation,in order to better achieve the strategic objectives of West-to-East transmission and national networking,more and more projects are using cross-linked hybrid transmission model.The use of line commuted converter high voltage direct current converter technology(LCC)is the most common,and its operating characteristics are excellent in traditional AC transmission.However,the inverter AC network side fault may lead to commutation failure,it would lead to continuous commutation failure or even converter station atresia in serious cases,endangering the safe operation of the system.The new capacitance commutation converter technology(CCC)can effectively avoid commutation failure.In this thesis,firstly,the traditional LCC HVDC system is modeled,the working process of the converter on both sides is analyzed in detail,the mathematical relationship between the commutation angle and the trigger angle is deduced,and the commonly used components and characteristics in the system are introducedThe.polar control in the control system is modeled,the characteristics of various control modes are analyzed,and a suitable combination is selected as the control strategy of this thesis.This thesis studies the failure fault of inverter side commutation in the system,analyzes its fault mechanism and puts forward several inhibitory measures according to the fault characteristics.On the basis of the original LCC system,a new CCC converter is formed by concatenating the capacitor between the converter and the converter transformer,the mathematical model of the structure is established,the differential equations of the system under steady state operation are deduced,and the commutation prediction module is designed for the fault design.By combining with the example of Hohhot-Liaoning HVDC Transmission project and transforming it into CCC HVDC system,the simulation verification in MATLAB/SIMULINK software environment is carried out,and the steady state operation,step response,one-phase grounding of converter AC system and two-phase short-circuit fault The CCC system with commutation failure prediction module is more excellent than the traditional LCC system,and its voltage and current recovery speed and anti-commutation failure ability are outstanding,which proves the feasibility of the model.This model has reference value for practical engineering.