Improved Discontinuous SVM Based Fault-Tolerant Control of AC/DC Converter for All-DC Offshore Wind Power System

An improved discontinuous space vector modulation (IDSVM) approach is proposed through analysis of key factors to impact fault tolerance control performance for the AC/DC converter in an all-DC offshore wind power system. The three main factors being studied are compensation ratios of active vectors, type of vectors used to resynthesize reference voltage vector and zero vectors distribution in time domain. Their effects are discussed from perspective of energy input, transmission and loss in the AC/DC converter. Three schemes using different compensation ratios for active vectors are compared, and scheme C using projections on current axis achieves better fault tolerance performance. In this paper, the distorted voltage vector is used to synthesize reference voltage vector and the healthy zero vector is redistributed in the twelve sectors. The former is beneficial to reduce three-phase current spikes and the latter helps to stabilize DC-link voltage. Performances of the improved modulation approach are verified on an experimental platform simulating the offshore wind turbine with single switch and multiple switch open-circuit faults. Its robustness and high performance are thoroughly evaluated.