Reactive compensation planning and control strategy for offshore wind farms using particle swarm optimisation

Large offshore wind farms are typically located far from the shore, and high voltage AC submarine cables along with onshore cables are commonly used to integrate them with the power grid at an onshore point of connection. These non-homogenous export lines have high capacitance, and the reactive power generated within them leads to overvoltages in the transmission system and limits the active power transfer capability of the wind farm. This paper proposes an optimal shunt reactor design and control strategy using the Particle Swarm Optimisation (PSO) algorithm to minimise active power losses in the export transmission system. The maximum size of the variable shunt reactor and the optimal tap positions for the onshore transformers and the variable shunt reactors located at the onshore and offshore substations are obtained for different active power generation levels. Subsequently, the results are compared with those obtained when the size of intermediate reactive compensation and its location along the non-homogenous export line are also optimised. Since optimisation of reactive compensation along the export transmission system also helps in the reduction of maximum cable loading, the impact of optimisation is also evaluated with respect to maximum cable loading in the export transmission system.