A Coordinated Control Strategy for Voltage Balancing at DC Unit Terminals in All-DC Systems

Voltage imbalance across DC terminals in the collection network arises when turbine wind speeds are not equal in series-connected offshore wind farm all-DC systems. To address this challenge, we propose a novel coordinated control strategy for achieving voltage balancing at the collection network terminals without additional hardware or software components. A comprehensive model of the offshore wind energy all-DC architecture is established, and the coordinated control strategy is analyzed from a system perspective. The control strategies for converters are examined in detail, including the VOC control strategy for the machine-side converter, the terminal voltage control strategy for the DC-DC converter, and the PQ/VF control strategies for the onshore DC-AC converter. The efficiency of the coordinated control strategy in maintaining voltage equilibrium at DC unit terminals within the series-connected collection network is demonstrated by the simulation results of an all-DC system model created with MATLAB/Simulink.