Consensus-Based Distributed Control of Offshore Wind Farms Connected via DR-HVDC

In offshore wind farms connected via diode-rectifier-based high-voltage dc systems, conventional distributed control strategies of wind turbine (WT) converters suffer from significant coupling between active and reactive power and frequency, leading to large oscillations in WT power and offshore frequency during transients. Upon theoretically analyzing this issue using a small-signal model, this work proposes a novel distributed control strategy to address it. Initially, we propose a specially designed consensus-based global average reactive power observer for each local WT controller, where the consensus algorithm is modified from its basic form to support an adjustable reactive power-sharing ratio. By comparing the observed and actual values of reactive power, a dynamically adjustable virtual impedance control is achieved, completely decoupling active and reactive power control. In addition, global reactive power values are also used in frequency droop control as local references, decoupling reactive power and frequency control while achieving proportional reactive power-sharing. Experimental results confirm that the proposed solution eliminates transient oscillations of reactive power and frequency compared to existing conventional and decoupled control methods.