A New Topology of Network Fault-Mitigation VSC- HVDC Transmission System
A VSC-HVDC transmission system is the network to meet all these challenges due to its operational flexibility, such as voltage support to ac networks, its ability to operate independent of ac network such as offshore wind farms, suitability for multi terminal HVDC network realization as active power reversal is achieved without dc link voltage polarity change. Present VSC-HVDC transmission systems rely on their converter station control systems and effective impedance between the point-of-common-coupling (PCC) and the converter terminals to ride through dc side faults. With present converter technology, the dc fault current comprises the ac networks contribution through converter free-wheeling diodes and discharge currents of the dc side capacitors. The magnitude of the dc-side capacitors discharge current decays with time is larger than the ac networks contribution.This project proposes a new breed of high-voltage dc (HVDC) transmission systems based on a hybrid multilevel voltage source converter (VSC) with ac-side cascaded H-bridge cells. The proposed HVDC system offers the operational flexibility of VSC based systems in terms of active and reactive power control, in addition to improved ac fault ride-through capability and the unique feature of current-limiting capability during dc side faults. The proposed HVDC system, in this project assesses its dynamic performance during steady-state and network alternations, including its response to AC and DC side faults.In this project PI controller is replaced with a fuzzy controller and the proposed topology is implemented in MATLAB/SIMULINK environment and the simulation results are observed.