Research On The Control Stragety Of VSC-HVDC Converter

VSC-HVDC is a new generation of DC power transmission technology based on IGBT and pulse width modulation technology, the active power and reactive power can be decoupled and controlled independently. This new generation of DC transmission technology has been widely used in modern power network areas such as interconnection of asynchronous AC power networks, connection of distributed renewable energy sources to power networks, power supply of isolated islands, and reconstruction of urban power networks. This thesis focuses on the control strategy of VSC-HVDC converter, Fuzzy Logic and Auto Disturbances Rejection Controller (ADRC) are introduced into the double-loop control strategy, a novel control stragety is presented and the simulation results verify the validity of the propsed control strategy.Firstly, the working principle and system configurations of VSC-HVDC are investigated. On the basis of analyzing the four-quadrant operation capability of VSC-HVDC system, its mathematical models under both three-phase static reference frame and two-pahse synchronous rotating reference frame are developed. This thesis analyzes the principle of Double Close-Loop Control Strategy. The outer loop creats the converter current reference, the inner loop regulates the output of the converter to control the active power and reactive power. Different types of control objectives give different types of outer loop, several types of outer loops are presented in this thesis.Secondly, the fuzzy logic control is introduced into the analysis and design of the control strategy of VSC-HVDC. The VSC-HVDC system is a non-liner non-decoulped control system, fuzzy logic is suitable in delaing with such systems. The principle of fuzzy logic is investigated and a novel type of fuzzy logic controller is developed to replace the original outer loop.Thirdly, this thesis investigated the application of Auto Disturbances Rejection Controller (ADRC) in the control stragety of VSC-HVDC converter. By combining the ADRC technology with the classic PI controller, the thesis presented a novel constant DC voltage controller. Both parameters variation within mathematical models of controlled objects and external disturbances will decrease system performance, ADRC technology is a good solution to this issue.Finally, the proposed control stragety is tested through Matlab/Simulink simulation. A typical system model is developed in Simulink, simulations under different working conditions are carried out. Results show that the proposed control stragety can fulfill its contrl objectives precisely and promptly under various working conditions.