Control strategy of a stand-alone variable speed wind turbine with integrated energy storage system using NPC converter

This paper presents a control strategy for a stand-alone power system comprising of a wind turbine and battery storage systems. The proposed control system consists of a back-to-back NPC converter controller and a bi-directional battery storage converter controller. The back-to-back three-level converter consisting of a machine-side converter and a load side inverter is used to fulfill several objectives. Firstly, the machine-side converter controller is used to extract the maximum power from the variable wind. Secondly, the machine-side converter controller ensures the maximum efficient operation of the interior type permanent magnet synchronous generator. Thirdly, the load-side inverter controller regulates the output voltage and frequency under wind and load variations. A bi-directional dc-to-dc converter is used to control the power flow of the battery storage system under different wind and load conditions. The proposed control system is implemented in MATLAB environment and simulation studies have been conducted for various wind and load conditions.