Coordinated operation in a multi-inverter based microgrid for both grid-connected and islanded modes using conservative power theory

In order to address the power quality enhancement in a given microgrid, independent control of reactive, unbalanced and distorted load current components, in a multi-inverter-based approach may be required. Therefore, this paper proposes a coordinated control strategy using the Conservative Power Theory (CPT) and assuming the contribution of all grid connected interfaces, especially those related to Distributed Generators (DG). For grid-connected operation, a coordinated current-controlled operation is proposed for supplying different load current components, improving power quality and consequently, minimizing the PCC voltage disturbances. In case of islanding operation, the microgrid may suffer from serious power quality problems due to the presence of nonlinear and/or unbalanced loads. To mitigate such current disturbances, a master-slave-based cooperative operation for DGs is presented. Since each primary source has its own constraints and topology, a supervisory control is considered to determine sharing factors for each current component. The microgrid system is controlled in abc-frame, offering a very flexible, selective and powerful load current sharing scheme, as demonstrated through digital simulations. The principles supporting the proposed control schemes are also discussed.