Decouple and Control Strategy for Variable Speed Variable Pitch Wind Energy Conversion System

Abstract

With the rapid growth of wind energy usage, the complexity of control systems used in the wind energy conversion systems (WECS) is also growing. As the nature of the wind is indeterminate, control systems must be able to deal with the stochastic nature of the wind and must be able to give the desired results. Thus, consideration of different types of advanced controllers for the WECS becomes important. One of the promising divide (decouple) and conquer (control) strategy using singular perturbations and time scales (SPaTS) for WECS has been used earlier for variable speed and constant pitch (VS-CP) wind model and using the linearization of the nonlinear model. In this project, the model of the variable speed and variable pitch (VS-VP) turbine wind energy system is considered for study. The designing and integrating the model of the VS-VP system is a bit more complicated and challenging than that of the VS-CP model. Further, the VS-VP system contains both mechanical and electrical components giving rise to the slow and fast dynamics, respectively and hence exhibiting the time scales. Briefly, the SPaTS technique helps in expressing the system with low-order, outer (slow) dynamics and inner (fast) dynamics. The inner dynamics is also called boundary layer correction. In this project we consider VS-VP WECS model for the decoupling process to obtain low-order slow and fast subsystems. Next, using the advanced optimal control methods, two low-order, closed-loop, optimal, slow and fast sub-controllers are obtained. A composite optimal controller is constructed using the two slow and fast sub-controllers and applied to the original nonlinear wind energy system. Comparisons are made between the results of the system using the full-order, optimal controller and the low-order, optimal sub-controllers to validate the SPaTS strategy.Finally, some conclusions and future work are included.