Optimized Secondary Control for Distributed Generation under Unbalanced Conditions

Control structure have a critical influence on converter-interfaced distributed generations (DG) under unbalanced conditions. In this paper, the relationship between amplitude of active power oscillations and reactive power oscillations is firstly deduced and the hierarchical control of DG is proposed to reduce power oscillations. Current references are generated in the primary control level and active power oscillations can be suppressed by the dual current controller. The secondary control reduces active power and reactive power oscillations by optimal model aiming at minimum amplitude of oscillations. The simulation results show that the proposed scheme with less injecting negative sequence current than traditional control method can effectively suppress oscillations of both active power and reactive power.