Operation of A Platform-less DC Collection System for Offshore Wind Farms with Reduced Curtailment Using Energy Storage

In this paper, a series connected DC wind energy collection topology is considered for offshore windfarms (OWF). Dual Active Bridge (DAB) with medium frequency transformer is used to reduce the size of the interface between the permanent magnet synchronous generator (PMSG) and the high voltage DC (HVDC) line. The series connection of the DAB output capacitors helps in achieving the platform-less operation by eliminating the need for a low frequency step-up transformer, but leads to a severe mismatch of the DAB output voltages due to the unequal wind power inputs at the wind turbines (WTs). Overvoltage at DAB output can be avoided by curtailment, i.e. operating the turbine away from the maximum power point tracking (MPPT) using WT inertia, which leads to loss of available energy. The possible use of ultra-capacitors (UC) to reduce the loss in energy is demonstrated in this work.