Research On Reactive Power Conpensation And Control Strategy For Series MTDC Transmission Systems

With economic development and power grid construction, the grid will inevitably require multi-power supplies and multi-infeed systems. And MTDC transmission is an effective way to solve this problem. In converter station the reactive power compensation and control have to satisfy the requirements of reactive power voltage in AC grid and coordination of technical problems related to the DC system. MTDC transmission causes more difficulties of reactive power compensation design. Series MTDC(S-MTDC) is one kind of MTDC, which is little researched both at home and abroad. Therefore, this paper discusses the basic principles, the reactive power theory, compensations and control strategies.First, this paper has theoretical analysis of S-MTDC in circuit structure, operation mode and control mode, as to reactive power theory of converter station. Thus it has proposed3kinds of reactive power balance modes and15kinds of configurations, which are compared and analyzed from a technical and economic point of view. According to the optimal solution, take the project of S-MTDC for example, based on±800kV Xiangjiaba-Shanghai Ultra HVDC transmission, full calculations of the converter station design have been done, verifying the switching of reactive power.Then, the paper discusses reactive power coordination and control strategy in the optimal balance. In main analysis of light load operation, over-load operation, the reducing voltage operation and fault operating conditions, the different power distribution caused reactive power control differences. Thus, it is proposed that a new plan of reactive power coordinated control of S-MTDC. Finally, a monopolar12pulse800kV S-MTDC model is built by the PSCAD/EMTDC simulation software, for the simulation verification of coordinated control strategy when DC power changes.