Internal Model-Based Cascaded Control Approach for Multi-Functional Grid Interactive Converters

Abstract

The concept of distributed generators (DG) and their control has been evolved as key area of research, to ensure the sustainability of a microgrid (MG). Design and implementation of a proactive cascaded control strategy is an effective method to make the MG more sustainable and resilient towards uncertainties. In this paper, a novel cascaded control strategy consisting of two degree of freedom (2DOF) PI and internal model controller (IMC) is proposed to effectively control the grid interactive converter (GIC). The proposed control strategy exploits the combined benefits of 2DOF-PI and IMC in improving the steady state and dynamic performance of the GIC. The primary function of the proposed control strategy is to effectively control the GIC in order to facilitate smooth power flow between MG and utility. In addition to this, the proposed control strategy enables the GIC to offer different ancillary services that include unbalanced load current compensation, reactive power compensation and harmonic current reduction. In order to achieve this multi-functional feature, appropriate reference currents are extracted and control strategy is implemented in synchronous reference (dq0) frame. An evaporation rate-based water cycle algorithm (ERWCA) optimization technique is employed to estimate the optimal design parameters of cascaded controller. The closed loop stability of the system is verified using frequency and time domain analyses for the estimated optimal design parameters. To show the effectiveness of the proposed control strategy, various case studies are considered and results are compared with existing methods.