Flexible power control of virtual synchronous generators under unbalanced grid voltage conditions

The stability problems of power electronics interfaced distributed generators with low inertia and damping can be well solved by the virtual synchronous generator technologies. However, when the grid voltages become unbalanced, oscillations in both the real and reactive power will arise with unbalanced voltages and currents of VSG being noticed. This paper proposed a flexible power control method of virtual synchronous generator under unbalanced grid conditions. Firstly the basic principle of the traditional virtual synchronous generator control method is briefly introduced. Then three different control strategies are presented based on control of negative-sequence voltage at PCC in d-q frame. Performance of these three control strategies are compared in PSCAD/EMTDC simulations. Finally, a RTDS-based real-Time digital and physical close-loop experimental test bed is built to verify the proposed control strategy furtherly.