DRU Based Low Frequency AC Transmission Scheme for Offshore Wind Farm Integration

Abstract

The low frequency AC (LFAC) technology is found to be a competitive solution for offshore wind farm integration. This article proposed an LFAC system with a hybrid onshore back-to-back (BtB) converter, for which the diode-based rectifier unit (DRU) and modular multilevel converter (MMC) based inverter are adopted. Then, this article also proposed corresponding control strategies for offshore wind turbines, where the DC link voltage control is implemented on the machine side converter, and the AC voltage of the offshore grid is controlled by the grid side converter based on the fixed reference frame. The small signal analysis for the whole system was carried out based on the equivalent circuit, and the small-signal stability is proven by calculated eigenvalues. And the system responses to typical operating conditions are investigated by time-domain simulations in PSCAD. Thus, the feasibility of the proposed scheme is verified.