Simulation Study And Power Control Of HVDC Flexible System

HVDC Flexible system is considered as a major development in HVDC technology, which is based on Voltage Source Converter. This technology shows a lot of technical advantage, thereby back-to-back connection in the power grids, mass capacity electrical source combined to the grid, power supply for isolated island and construction of MTDC system. The technology of HVDC Flexible has been considered as one of the focus issue about the study of the modern power grid, the research of operation and control problem about this technology in the power grid area has important theoretical significance and practical value.Firstly, with basic theory analysis of HVDC Flexible technology, the dynamic mathematical model is developed under the dq0 reference frame for the simulation study in the power grid area, through correlative analysis about the control variable and controlled variable in the equation, the controllers corresponding to each converters are designed, and simulation tests are carried out to prove the correctness of the dynamic mathematic model and effectiveness of the proposed control system.Based on the study of two sides HVDC Flexible, the control problem of the power flow of the VSC-MTDC technology is developed in this paper. The multi-terminal constant DC voltage controller with voltage droop scheme is proposed. The simulation tests of the VSC-MTDC system about several typical circs are carried out to prove the effectiveness of the controller. Further research is carried out on the operation of VSC-MTDC system.At last, study on supplying unbalanced load with HVDC Flexible system is researched. Symmetrical component method is used to analyze the unbalanced output voltage aroused by unbalanced loads, and a complex rectification method is proposed. As above, the effectiveness of the proposed rectification method is proved by simulation test.