System wide-band oscillation analysis of fractional frequency offshore wind power systems

Abstract

The fractional frequency offshore wind power system (FFOWPS) is a core technology for the long-distance transmission and integration of the large-scale offshore wind power. However, the risk of wide-band oscillation in the FFOWPS has become increasingly prominent due to the inevitable presence of the power electronic devices. The traditional admittance of the frequency converter, which is a crucial component in the FFOWPS, may contain right-half-plane (RHP) poles when operating under various control modes. To address this deficiency, this paper establishes a four-port small-signal admittance model of a back-to-back frequency converter and demonstrates its interconvertibility with the traditional model. On this basis, the wide-band oscillation analysis method for the FFOWPS is proposed, which explicitly describes the influence of the industrial frequency system, the fractional frequency system, and their coupling interactions on system stability. Simulation results in MATLAB/Simulink verify the proposed stability analysis method, highlight stability misjudgements associated with the traditional admittance, and analyse the impact of the coupling terms on system stability.