A Robust CCS Predictive Current Control for Photovoltaic Energy Storage System Based on a Nonlinear Disturbance Observer

Abstract

This article introduces a new control strategy for a bidirectional DC/DC converter used in photovoltaic energy storage systems (PV-ESSs), aimed to address the DC bus voltage deviation problem. The purpose of this paper is to design and practically implement a robust continuous control set predictive current control (CCS-PCC) method based on a nonlinear disturbance observer (NDO) to tightly regulate the common DC bus voltage in islanded DC microgrids. The CCS-PCC controller is used to replace the current loop PI controller, which effectively overcomes the shortcomings of the traditional linear lag control and improves the dynamic performance of the system. At the same time, the CCS-PCC method solves the inherent defect of finite control set predictive current control (FCS-PCC), where the switching frequency is not fixed. It effectively reduces the current ripple and realizes constant frequency control. In order to effectively suppress the DC bus voltage fluctuation during transients, the nonlinear disturbance observer is designed and combined with CCS-PCC. The feedforward method based on the NDO was utilized to enhance the disturbance rejection capability of the system. The simulation and experimental results show the feasibility and effectiveness of the proposed CCS-PCC+NDO approach, both during transient and steady-state operating conditions.