A Universal Multiple Inverter Control Architecture with Droop For Unbalanced Distribution Grid

The ever-increasing integration of distributed energy resources (DERs) using three-phase voltage source inverters (VSI) results in the need for better management of VSIs. For example, these VSIs are now required or capable of providing the required positive and negative sequence (PNS) components in an unbalanced power grid. This is achieved by developing a dedicated control strategy for PNS voltages and currents of grid-forming and grid-feeding VSIs. The grid-forming and grid-feeding VSIs can operate in a grid-connected mode as well as islanded mode as a microgrid. These multiple VSIs utilize existing distribution feeders which are part of an unbalanced system in terms of load, and feeder-impedances. In this work, a new robust droop control based approach is proposed to support multiple VSI operation in both grid-connected or islanded modes of operation. To achieve the fault ride-through capability of VSIs, a current limiter is also proposed in the dq-frame accounting for the PNS currents during unbalanced fault scenarios. The simulation results in MATLAB/Simulink confirm the effectiveness of the proposed control method and current limiting strategy.