Advanced Modelling and Assessment of Conventional and Multi-Level Unified Power Quality Conditioner (UPQC) Performance

In the domain of power quality enhancement, both conventional and dual compensation strategies have been widely employed in Unified Power Quality Conditioners (C-UPQC and D-UPQC). However, their comparative analysis often lacks depth, particularly under varying grid conditions. This study introduces an advanced approach by extending the scope to a Multi-UPQC configuration, which integrates multiple compensation units to operate in coordination. The paper establishes small-signal models in the dq-axis for both conventional, dual, and multi-UPQC systems, while accounting for the effects of grid impedance and phase-locked loop (PLL) dynamics. A comprehensive performance analysis is conducted under both steady-state and dynamic scenarios, including abrupt changes in grid voltage and load conditions. The results reveal that the D-UPQC demonstrates superior dynamic response under transient conditions, whereas the C-UPQC and D-UPQC show varying capabilities in harmonic suppression. Notably, the impact of grid impedance on load voltage quality is more pronounced in the C-UPQC, whereas the Multi-UPQC system effectively overcomes this limitation by distributing the compensation effort across multiple nodes. This collaborative compensation enhances reliability, expands coverage area, and improves both voltage regulation and harmonic mitigation. The study’s insights offer valuable guidance in selecting the most suitable compensation strategy for specific grid applications. Experimental validations confirm the accuracy of the proposed comparative framework and the superior adaptability of the Multi-UPQC system.