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Active power angle droop control per phase for unbalanced 4-wire microgrids

Most low voltage microgrids have four wires and operate mainly unbalanced. This paper considers a new droop control per phase of a four-wire microgrid to solve the problems associated to unbalanced operation (e.g. high neutral current). Unlike the conventional approaches, in this work, the active power per phase of each converter is shared varying the output voltage angle of each inverter phase. The proposed control system is based on a hierarchical control structure. The inner control loop of the inverter output voltage is implemented using resonant controllers, applying an active damping strategy to improve the system response. On the primary control loop, the angle droop control strategy is applied to share the active power per phase, according to the nominal ratings of the generation units. Then, a secondary control loop is utilised to restore the unbalance of the voltages to the nominal values. Experimental results obtained with a 3 kW four-wire microgrid prototype are presented and discussed to validate the proposed control system.