A hierarchical control scheme for compensating voltage distortions in an inverter based microgrid

Nowadays increasing in nonlinear loads intensifies harmonic problems and voltage distortion in distribution systems. With appropriate control of Distributed Generation (DG) resources in a Micro Grid (MG), it is possible to enhance the MG power quality. This paper proposes a hierarchical control method for Inverter Based Distributed Generators (IBDGs) to compensating voltage distortions such as: voltage harmonics, voltage unbalance and voltage sag and swell in Sensitive Load Bus (SLB).This method consists of two control level of primary and secondary. The secondary control proposes a selective harmonic compensating method and voltage unbalance compensation appropriately according to DGs impact on harmonic resonances. Some buses have more participation in exciting of the MG resonance modes. Therefore, larger harmonic compensation factors are considered for the IBDGs that are near to these buses. For the other IBDGs, the voltage unbalance compensation factor is selected bigger. On this basis, the Participation Factor (PF) of buses in different resonances is identified by network modal impedance analysis then, the compensation share of DGs would be prioritized accordingly. The primary control level includes of voltage controller, current controller, virtual resistor and DGs load compensation block. Effectiveness of the proposed control scheme is demonstrated through simulation studies.