Cooperative Control of Multi-Master-Slave Islanded Microgrid with Power Quality Enhancement Based on Conservative Power Theory

Cooperative control of power converters in a microgrid offers power quality enhancement at sensitive load buses. Such cooperation is particularly important in the presence of reactive, nonlinear, and unbalanced loads. In this paper, a multi-master-slave-based control of distributed generators interface converters in a three-phase four-wire islanded microgrid using the conservative power theory (CPT) is proposed. Inverters located in close proximity operate as a group in master-salve mode. Slaves inject the available energy and compensate selectively unwanted current components of local loads with the secondary effect of having enhanced voltage waveforms while masters share the remaining load power autonomously with distant groups using frequency droop. The close proximity makes it practical for control signals to be communicated between inverters in one group with the potential to provide rapid load sharing response for mitigation of undesirable current components. Since each primary source has its own constraints, a supervisory control is considered for each group to determine convenient sharing factors. The CPT decompositions provide decoupled current and power references in abc-frame, resulting in a selective control strategy able to share each current component with desired percentage among the microgrid inverters. Simulation results are presented to demonstrate the effectiveness of the proposed method.