Robust Nonlinear Controller Design for On-Grid/Off-Grid Wind Energy Battery-Storage System

This paper investigates the design of a unified robust nonlinear multi-input-multi-output controller for a wind energy battery-storage system. The system can be operated either in grid-connected mode or stand-alone mode. Feedback linearization control design method is used to find the controller equations. The main advantage of the proposed control strategy over the existing methods is that only a single controller is used to control the system regardless the mode of operation. With the new approach, the controller is designed so that the grid contribution is significantly reduced and the battery can provide a backup energy or store the surplus wind energy efficiently. In addition, the dc-link voltage and load power are regulated by adjusting the charging and discharging cycle of the battery through a bi-directional buck-boost dc/dc converter in contrast to existing methods where the dc-link is regulated by the grid-side converter. The robustness of the proposed controller is evaluated in simulation with various types of loads, including unbalanced load and dynamic load. The results show that a good performance in closed loop is achieved.