A Coordinated Control Scheme for Improving Voltage Quality Using Power Electronics Interfaced DGs

Recently, increasing of non-linear loads in the power distribution network has been increased harmonics in these networks. The harmonics problems get worse and complicated by installation of power factor correction capacitors and filters. But the Distributed Generations (DGs) interface inverters with properly control can help to improve power quality, harmonic compensation and voltage unbalance. Until now, much research has been performed in identifying harmonics and compensation by DGs. This paper presents a hierarchical control method by DGs to compensate voltage disturbances on the Sensitive Load Bus (SLB) in a Micro Grid (MG), which includes two levels of control: primary and secondary. In secondary control has been proposed an appropriate non-uniform compensation method of harmonics and voltage unbalance, based on impact of DGs in the resonance frequencies. With doing analysis of the network modal impedance and its results, the DGs with higher participation factors will have greater duty in compensation of the stimulus harmonics, and the DGs that being less engaged with stimulating of harmonics will have greater portion in compensation of the network voltage unbalance. The primary control also includes current controller, virtual resistance and load compensation controller. The simulation results show the effectiveness of the proposed control system.