Distributed-Diode-Rectifiers-Based Offshore Wind Power MVDC Direct-Transmission System

An offshore wind power medium-voltage direct-current (MVDC) transmission system based on distributed diode rectifiers (DRs) is proposed to realize the DC transmission of offshore wind power and eliminate offshore platforms. A coordinated control strategy between wind turbines (WTs) is proposed to greatly reduce the transmission voltage ripple and current ripple for this system. A small-signal state-space model for the WT line-side converter control system is established. The less damped terms in the control system are found through system eigenvalues, and the stabilization control method is further proposed. A joint control strategy between the onshore converter station and offshore WTs is proposed to achieve system fault ride-through. This strategy can quickly transmit the onshore AC grid's fault information to each WT and consume unbalanced power by the dc choppers inside WTs. The simulation results in PSCAD verify the effectiveness of the proposed control strategy.