Three-level control strategy for minimizing voltage deviation and flicker in PV-rich distribution systems

Abstract

Voltage deviation (VD) and voltage flicker (VF) are considered common operational problems associated with high photovoltaic (PV) penetrated distribution systems. In this paper, an optimal control strategy is proposed for minimizing VD and VF in PV-rich distribution systems. The control strategy is based on proposed analytical expressions that minimize both voltage problems by optimizing the smart functions of the PV inverters and control devices simultaneously. The proposed analytical expressions are formulated based on voltage sensitivities with respect to the active and reactive power injections of PV. Specifically, a three-level control strategy with different time resolutions is proposed to significantly alleviate voltage deviation/flicker while minimizing PV active power curtailments and tap movements for transformers. These control levels are (1) local control (LC), (2) area control (AC), and (3) coordinated control (CC). LC provides rapid local control actions to minimize VD and VF, AC minimizes VD within the corresponding area individually, and CC plays a vital role to coordinate between the various control units. The proposed control strategy is assessed using high PV penetration with realistic high-resolution very-variable solar radiation datasets (10 ms). To demonstrate the accuracy and efficiency of the proposed analytical expressions, the calculated results have been compared with existing methods. Results demonstrate that the proposed control strategy effectively coordinates between the various voltage control units while minimizing VD and VF.