Optimized Power Redistribution of Offshore Wind Farms Integrated VSC-MTDC Transmissions After Onshore Converter Outage

The increasing penetration of renewable sources, particularly wind energy, has provided the power system with large-scale clean electricity. For integrating gigawatt offshore wind energy, voltage source converter (VSC) based multiterminal HVDC transmission is the prospective technology with flexible control characteristics. Most of the papers so far have dealt with improving the frequency performance caused by an ac system disturbance, and only a few deals with the influence of dc system converter outage on frequency performance. However, the converter outage will bring successive power impulses to the onshore ac grids. This paper presents an optimized power redistribution method to enhance the frequency performance of onshore ac grids. The two scenarios of power redistribution after converter outage are analyzed: self-distributed type and nonself-distributed type. For the self-distributed scenario, the optimized power redistribution method involves three steps: sensitive cluster identification, optimized power redistribution calculation, and dc grid operating point setting. For the nonself-distributed scenario, a combined offshore wind farm control strategy with emulating inertia control and auxiliary pitch angle control is proposed to alleviate the adverse effect of the transferred surplus power on asynchronous grids. Simulation verifications are carried out in a modified New England 39-bus system with seven terminal VSC-HVDC transmission system.