Date of Award


Publication Type

Master Thesis

Degree Name



Electrical and Computer Engineering


Maher Azzouz




Inverter-interfaced distributed generators (IIDGs) generate fault currents that are different from those generated by conventional synchronous generators (SGs). As a result, commercial relays—that utilize current-angle-based phase selection measurements—misidentify faulty phase(s), which adversely impact the grid resiliency and reliability. In this thesis, a new control scheme is proposed to regulate the sequence components of the IIDG currents during unbalanced faults to ensure accurate fault type classification by commercial relays. The proposed controller controls the positive-sequence and negative-sequence currents in the dq-frame with a decoupled synchronous reference frame (DDSRF) based phase-locked loop (PLL) for components extraction and synchronization. It also uses a second order generalized integrator (SOGI) based PLL to synchronize the zero-sequence components. This scheme forces the angles of the negative-sequence and zero-sequence fault IIDG currents to behave like those of an SG while preserving the inverter’s current limits. This leads to proper fault type classification. The proposed control scheme pertains to three-wire IIDGs as well as four-wire IIDGs, which are common in low-voltage distribution networks. A performance evaluation using time-domain simulations is used on a benchmark network to confirm the success of the proposed control scheme under different fault conditions.