| Our country has planned to build several HVDC projects in order to match the requirements of economy. The stability problems of HVDC systems will become important. This thesis aims at controlling HVDC systems to improve the stability of power systems.HVDC transmission systems are a typical nonlinear and time-varying control systems, which poses difficult control problems and complicated control strategies. PI controllers are traditionally used in HVDC system. Although these controllers have been operating satisfactorily for many years, the results are not perfect.With the development of control theory and technique, decentralized adaptive control technology is gradually showing its superiority. It is mainly used for the difficult control problems, which can't be solved by traditional ways. It's high time to introduce decentralized adaptive control techniques into the HVDC control filed.This paper presents a design approach to decentralized robust adaptive controllers for HVDC. Utilizing backstepping procedure, general expression of control strategy for HVDC converters is acquired. The control strategy can restrain the nonlinear uncertainty through injection of nonlinear damping terms in virtual controllers. The proposed decentralized adaptive control scheme guarantees that all the signals in the closed-loop system are bounded in the presence of high order interconnections and bounded disturbances. The controllers obtained only use localmeasurements, which makes it practicable. Moreover, the control law is independent of transmission network parameters. Simulation results acquired by using NETOMAC software show that the controllers work better than the traditional PI controllers for the stability of HVDC system.This work was supported by the National Key Basic Research Special Found of China under grant No.G1998020312.
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