A Novel Sequence-Based Unified Control Architecture for Multiple Inverter Modes of Operation in Unbalanced Distribution System

Abstract

Control of multiple inverters in the distribution grid can be achieved by adopting appropriate droop laws. However, in an unbalanced power distribution system with single-phase and two-phase laterals, droop-based control methods fail thus requiring dedicated inverter control methods that can supply required positive and negative sequence (PNS) components. In this article, a unified control architecture is proposed for stable multiple inverter operation that can improve the accuracy of active and reactive power sharing alongside maintaining the voltage and frequency of the system close to the nominal values. The proposed control strategy further ensures the supply of required negative sequence components to maintain balanced steady-state system voltage and mitigate the active power ripples during unbalanced faults. The unified control architecture is devised through a systematic definition of steady-state operating modes and the interaction among hierarchical grid entities, facilitating the coexistence of PNS controllers to meet the defined objective. The results are verified using a real-time simulator-based multi-rate model-in-the-loop set-up. Furthermore, appropriate communication network latency is considered for the verification of the performance of the proposed PNS controller. The verification for various grid events confirms the capability and effectiveness of the proposed control architecture, and suitability for 100% inverter-based grid operation.