A robust control algorithm for a multifunctional grid tied inverter to enhance the power quality of a microgrid under unbalanced conditions

This paper proposes a robust control algorithm for a Multifunctional grid-tied inverters (MFGTI) under unbalanced load and main voltage conditions. The proposed algorithm uses the instantaneous power theory to design the MFGTI controller. A Positive Fundamental Components Estimator (PFCE) is used to estimate the undesired components of the load current such as harmonics, reactive current, and negative sequence component. The PFCE is a lightweight open loop algorithm. Hence, a good robustness is achieved with a lower computation burden. Furthermore, a new sliding mode controller (SMC) is used as a DC bus voltage regulator to enhance the dynamic performance and robustness against parameter variation. The MFGTI is connected at the Point of Common Coupling (PCC), interfacing the microgrid to the main grid. Alongside the active power injection, the proposed control algorithm allows the MFGTI to compensate reactive power, mitigate harmonics, and balance the load. Thus, the microgrid will meet the different power quality standards. An experimental prototype is designed to verify both the performance and robustness of the control algorithm. The attained results confirm the validity of the proposed algorithm.