Multi-objective integrated VSG control strategy under unbalanced conditions

Purpose In the emerging power system dominated by photovoltaic and wind power generation, the virtual synchronous generator (VSG) has become an effective control approach because it can emulate synchronous inertia and damping. However, unbalanced loads and power grid faults often lead to voltage and current asymmetry. Under such unbalanced conditions, traditional VSG control fails to maintain satisfactory performance. To address this issue, this paper aims to propose a multi-objective integrated VSG control strategy. Design/methodology/approach This paper first analyzes the principles of the traditional VSG control and illustrates its limitations under unbalanced conditions using MATLAB/Simulink simulations. Next, a mathematical analysis of the VSG output power under unbalanced conditions is performed, leading to the derivation of oscillation expressions for both active and reactive power. Finally, considering the control objectives in both islanded and grid-connected modes, a negative-sequence voltage calculation module is developed. A closed-loop negative-sequence voltage control is further introduced to ensure accurate tracking of the voltage reference. In addition, a sequence component extraction module is incorporated and coordinated with the proposed multi-objective integrated VSG control. Findings Under unbalanced conditions, achieving simultaneously balanced voltage, balanced current, constant active power and constant reactive power is inherently conflicting. The proposed integrated VSG control addresses this issue by deriving the reference values for the negative-sequence voltage under different control objectives. Compared to the traditional VSG control, it can reduce voltage unbalance factor below 2% in islanded mode. In grid-connected mode, it can suppress reactive power fluctuations by up to 91%, active power fluctuations by up to 75% and current unbalance factor (IUF) below 2%. The proposed control strategy is validated through both simulation and hardware experiments, demonstrating its effectiveness and feasibility. Originality/value Compared to the existing VSG control, the proposed VSG control strategy is applicable to both unbalanced load and unbalanced grid voltage conditions. It significantly reduces voltage and current unbalance and substantially mitigates active and reactive power fluctuations under unbalanced conditions, demonstrating strong disturbance rejection performance.