Research On Coordinated Control And Commutation Failure Of Multi-terminal Feed Direct Current System

There’s a polarity distribution with energy and loads in China. HVDC has become an important way for remote and large-capacity power transmission as well as regional networking since its huge power transmission capability.In recent years, HVDC including UHVDC transmission projects have been in construction and put into operation in large-scale in China, forming a multi-terminal feed direct current because a plurality of AC systems are connected through a DC line. MTDC is applied to deliver power to a plurality of load center, meeting the large capacity, ultra-long haul transmission requirements.MTDC system has a plurality of converter station and there’s interaction of control among stations. Therefore all converter stations must be controlled by coordination. Commutation failure is the most common fault in HVDC, the mechanism and factors that cause commutation failure will be different from the traditional two-terminal HVDC. In view of this, the coordinated control and commutation failure are researched in MTDC system and the feasibility is proved through the steady state and transient characteristics analysis.Firstly, began with background and significance of this paper, the development ofHVDCisgeneralized and the present researchsituation of MTDCand commutation failure are concluded. The followinganalyzetopologies of MTDC, giving the main wiring of converter station and how converter stations connect. Then control modes of MTDC are analyzed, propose s coordinated control strategy based on current margin. A correspond model is built in PSCAD/EMTDC. The follow chapter gives extinction angle formulas of inverter stations by mathematical method using equivalent model, analyzing commutation failure mechanism and affected factors in MTDC. Finally,the steady state and transient characteristics of MTDC system are analyzed, respectively. The startup of system, steady operation, coordinated current control, fault on AC side and fault on DC line are simulated and analyzed, through which to verify the effectiveness of current coordinated control strategy and factors that lead to commutation failure in MTDC.