A multi task microgrid inverter based instantaneous Power Theory in islanded and grid-connected modes

This paper develops a flexible control strategy for DG inverters in a microgrid application with load current decomposition based on Instantaneous Power Theory (PQ). For grid connected mode of operation, the control strategy simultaneously supply all or part of the load current components allowing the DG system to inject its available energy, as well as to work as an active power filter, mitigating load current disturbances and improving power quality. Being able to supply the total load current by inverter allows a smooth transition between grid-connected and islanded modes of operation with zero current injection by the grid to guarantee an uninterrupted power supply to the critical loads within the microgrid. For the islanded mode of operation a multi loop control method with preservation of the grid-connected control system is developed to regulate load voltage/frequency in a wide range of load conditions. The control strategy is implemented in abc-frame. The principles supporting the developed control strategy are discussed and analyzed offering a very flexible, selective and powerful strategy for the DG control system, and the effectiveness of the control is demonstrated through digital simulations conducted by PSIM.