Dual-module VSG control strategy under unbalanced voltage conditions

The virtual synchronous generator (VSG), as a grid-connected technology, has gain more and more attention because of its unique merits including its ability to reshape inertia and damping. These merits enable renewable energy to be smoothly integrated into the grid. Unbalance between three-phase voltage in the steady state is a common phenomenon in the grid, which distorts the output current of the VSG. However, on many occasions, inserting symmetrical current into the grid is necessary. To solve this problem, a dual-module VSG control strategy is proposed in this paper. Through this strategy, the positive and negative sequence output powers of the VSG can be correctly identified and separately controlled. Then the output current can be kept symmetrical by controlling the negative sequence output power of the VSG to be zero. Finally, the proposed strategy is verified by simulation and experimental results.