An improved offshore wind turbine to MVDC grid interface using high frequency resonant isolation and input power factor control

This work introduces a new approach using high frequency (HF) isolation transformers with a series resonant power transfer mechanism for interfacing next-generation offshore wind turbine generators (WTGs) to medium voltage DC (MVDC) collection grids, a necessity for the continued development of offshore wind resources as farms are sited further out to sea. Analysis of the proposed approach is provided, as well as a practical design example. Detailed simulation results demonstrate converter operation from full rated power down to 25% rated power. The WTG displacement power factor is found to be 0.96 lagging. The three-phase multilevel input rectifier allows 5 times reduction in DC link capacitance over the previous per-phase approach. Near-sinusoidal WTG and transformer currents, continuous output currents, stiff DC link voltages and zero current switching (ZCS) in the HF inverter are all observed in simulation. Experimental results from 50 W prototype single-phase multilevel input rectifier stage corroborate corresponding to simulation results, with measured DPF of 0.92 lagging.