Distributed hierarchical control structure for voltage harmonic compensation and harmonic current sharing in isolated MicroGrids

In this paper, a distributed hierarchical control structure is proposed for compensating voltage harmonics of Sensitive Load Bus (SLB) and sharing current harmonics of load current among Distributed Generation (DG) units in isolated MicroGrids (MGs). In this structure, each DG has primary and secondary controller implemented locally. In the primary control level, a method is proposed for voltage harmonic compensation at SLB and sharing the compensation workload, which is based on non-fundamental apparent power, and directly takes into account the rated capacity limitation of DG inverter. Furthermore, in this level, another method is proposed for accurate harmonic current sharing among DGs which is based on circulating currents. The proposed method is capable of removing harmonic current sharing error without using any knowledge about MG topology and also impedances of distribution lines and loading conditions. Moreover, the effect of the applying proposed method on the amplitude and quality of DG output voltage waveforms will be insignificant. The secondary control level transmits the reference control signals to the primary control level in order to decrease the voltage harmonics at SLB and share harmonic currents among DGs. Details of designing control system parameters are presented and simulation results are given to show the efficiency of the proposed structure.