Dr. Muhammad Farooq Umar successfully defended his Ph.D. Dissertation

The primary focus of this dissertation is to address the challenges for stable and resilient operation of low inertia power systems (LIPS) dominated by grid-forming inverters (GFMI) and grid-following inverters (GFLI) with inherent heterogeneity. A forced enclave homogenization (FEH) scheme is proposed to enforce coherent dynamics within the heterogeneous cluster. This control method involves autonomously determining the equivalent inertia of the cluster and then adjusting the droop characteristics to enforce coherency in the heterogeneous cluster. The proposed FEH scheme is validated via multiple case studies that involve various levels of grid disturbance and cluster reconfigurations. It is demonstrated that the proposed FEH scheme is able to effectively enforce coherency in heterogeneous cluster of GFMIs and enables accurate representation of multiple GFMIs in a grid cluster with a “single machine” model. The conventional reduced-order model technique for the network of GFMIs fails to mimic the true dynamics of the heterogeneous network. The proposed insightful aggregated reference model finds applications in different LIPS analysis and operational domains as discussed briefly in this dissertation.

Furthermore, this dissertation extends the proposed coherency enforcement control scheme during fault and post-fault conditions in LIPS, incorporating an effective fault detection logic (FDL). The main contribution here is enabling the resilient operation of GFMIs in LIPS during a large-scale disturbance such as a short-circuit fault. The proposed scheme prevents transient instability by inhibiting the acceleration of the voltage angle of GFMIs during short-circuit faults.  Moreover, the proposed control scheme facilitates a seamless transition from fault to normal operation. The challenges for the GFLI integrated with weak and ultra-weak LIPS are addressed by proposing an adaptive model predictive control (AMPC) scheme. The AMPC leverages inherent damping characteristics of inverter-side current feedback (ICF) during weak LIPS, integrating a dual-state variable feedback approach with the MPC framework. This approach minimizes tuning efforts and efficiently dampens resonance within three grid cycles. Overall, this dissertation contributes to the understanding and enhancement of the stable and resilient operation of LIPS dominated by GFMIs and GFLIs in various operational conditions.