Steady State Characteristics of Diode Rectifier Unit based Grid-Forming Offshore Wind Power AC System

Nowadays, the high voltage direct current (HVDC) transmission system is the typical scheme for long-distance offshore wind power integration. The diode rectifier unit (DRU) can further improve the economy and reliability of the HVDC system. In this paper, the steady state characteristics of the offshore wind power AC system based on the grid-forming wind turbine (WT) and the DRU are analyzed. First, the topology of the DRU based offshore wind power integration system is introduced, and the grid-forming WT control strategy with the reactive power-frequency (Q-f) droop is elaborated. Then, the mathematical model of the DRU station is derived, and the power flow equations are expressed. On this basis, the steady state power flow calculation method of the offshore wind power AC system is proposed. The power flow iteration is according to the unbalanced reactive power of the DRU station AC bus, and the Q-f droop control characteristics of the grid-forming WT are considered. Finally, the steady state characteristics of the offshore wind power AC system are analyzed in the DRU based case system.