Research On VSC-HVDC Using In Liaoning Power Gird

With the development of industry and commerce of the city and the improvement ofpeople’s living standard, urban power grid for power supply capacity and quality ofpower supply put forward very high requirements. Especially in densely populated majorcity, Power grid has received the unprecedented challenge. VSC-HVDC is a new kind ofdc power transmission with VSC and PWM technology. Applicable to renewable energygrid, distributed generation grid, passive network power, asynchronous AC gridinterconnection and other fields. This paper focuses on the mathematical model andVSC-HVDC control strategy, and simulation of the technology in Liaoning power grid.1. Based on the mathematic model of VSC-HVDC in abc three phases static coordinatesystem, the per-unit mathematical model and the equivalent circuit diagram ofVSC-HVDC in d-q synchronous rotation coordinate system are established. Thedouble-loops and direct-current control strategies of VSC-HVDC is studied， the currentinner loop controller based on the current state feed-forward and decoupling theory isdesigned, and then the outer loop control strategy (e.g. constant DC voltage control,active and reactive power control and frequency control). The control strategy for gridintegration of large DFIG-based wind farms using VSC-HVDC is detailed studied. Inorder to control wind farm side AC voltage amplitude and frequency constant value, andthen automatic collect wind power to transmission to grid side converter station.2．Studied the asymmetric system failure occurs, the transient mathematical model ofthe VSC-HVDC system，and biordered inner current control strategy of VSC-HVDC, andouter voltage control strategy of suppression of negative sequence current and2times thevoltage harmonics on DC side.. For220kV bus short-circuit current superscalar issueexists in Anshan, propose the use of VSC-HVDC suppress short-circuit current. Verifiedthe effect of inhibiting the short circuit current by simulation that the proposed method.4. Perform load forecasting and analysis of the balance of power grid structurecharacteristics in Dalian. Combined with environmental factors in Dalian, use BPA toflow calculation under both normal and special way to calculate in Dalian areas. Foundweaknesses in the regional power grid and presents the problems of urban power grid andsouth urban power grid.5. Combined with the results of the trends and the grid structure characteristics in Dalian. Using BPA to flow calculation under both normal and special way to calculate inDalian areas, verify the role of improving the power supply capacity and the reliability ofVSC-HVDC. Verify that the VSC-HVDC in improving systems transient stability,providing reactive power and voltage support and improve the ability of the systemvoltage stability by fault simulation.