Comprehensive control strategy of virtual synchronous generator under unbalanced voltage conditions

The virtual synchronous generator (VSG) is emerging as an effective approach for controlling converter to mimic the traditional synchronous generator (SG). VSG can provide virtual inertia, handle both reactive and active power, which is grid-friendly for integrating distributed generations. Generally, when grid voltage is unbalanced, the negative sequence voltage components will appear. Due to traditional VSG control strategy does not consider the negative sequence components and cannot eliminate them, thus it will lead to current unbalance and power oscillations. To address these problems, a comprehensive control strategy of VSG under unbalanced voltage conditions is proposed. Herein, the basic principle of VSG and inherent reasons for VSG current unbalance and power fluctuation are demonstrated with quantitative analysis. The cascaded control framework and design process of the comprehensive control strategy are presented, integrating the traditional VSG control algorithm, novel current reference generator and typical current regulator. Additionally, related critical issues such as sequence components extraction and control parameter design are discussed. The proposed control strategy can flexibly meet different operation demands, including current balancing and suppression of active power or reactive power oscillations. The validity and effectiveness of the proposed control strategy are verified with simulation and experimental results.