Current and power quality multi-objective control of virtual synchronous generators under unbalanced grid conditions

In recent years, with the large-scale application of distributed power sources in the power grid, the power grid is moving toward low inertia and low damping. The virtual synchronous generator (VSG) has become a hot topic for scholars since it can simulate the moment of inertia, damping and frequency modulation of synchronous generators. Due to its unbalanced load distribution and the random variation of power loads, grid voltage is asymmetrical. Under grid voltage asymmetry, a VSG experiences output current imbalance and power oscillation. The grid current imbalance further reduces the transformer's three-phase voltage, which makes it unequal, cyclic, and very easy to cause electricity accidents. Aiming at this problem, this paper proposes three modes of current balance, reactive power balance and active power balance without changing the characteristics of VSGs. The output current balance and power are constant when the grid voltage is asymmetrical. The effectiveness and feasibility of the control strategy are verified by simulation and experimental results, which provides an effective scheme for balanced and stable operation of the grid.