Control of energy conversion in a hybrid wind and ultracapacitor energy system

Abstract

In this thesis the design and implementation of a control strategy for interfacing a hybrid wind and ultracapacitor energy system is presented. The proposed system consists of a Permanent Magnet Synchronous Generator (PMSG)-based wind turbine and an ultracapacitor storage element. The PMSG-based wind turbine is connected to a DC (direct current) bus through an uncontrolled rectifier and a DC-DC boost converter; the ultracapacitor is interfaced to the DC-bus using a bidirectional DC-DC converter. In a wind energy system, because of the unpredictable nature of wind speed, a Maximum Power Point Tracking (MPPT) algorithm is essential for determining the optimal operating point of the wind turbine. This work proposes a new and simple MPPT algorithm based on hybridization of the Optimum Relation Based (ORB) and Particle Swarm Optimization (PSO) methods. The proposed MPPT is advantageous in being sensorless, converging quickly and requiring no prior knowledge of system parameters. In addition, a Linear Quadratic Regulator (LQR) strategy has been applied in designing the DC-DC converter controllers because of its systematic procedure and stability advantages and simplicity. Two controllers based on the LQR method have been designed and implemented. One controller forces input current of the boost converter to track the optimal reference current generated by the proposed MPPT algorithm. The other regulates the DC-bus voltage at a desired level. The regulation is accomplished by controlling the bidirectional converter interfacing the ultracapacitor and the DC-bus. The proposed energy system and its controllers have been simulated in MATLAB/Simulink and implemented using a TMS320F2812 eZdsp board. Simulation results indicate that the proposed PSO-ORB MPPT algorithm average efficiency is 99.4%, with harvested electrical energy 1.9% higher than the conventional OTC and ORB MPPT algorithms. The simulation results also demonstrate the effectiveness of the proposed LQR controllers in obtaining good tracking and their ability to quickly restore the system to its nominal operating point when it is exposed to a disturbance. The simulation results are highly comparable with the experimental results that have successfully verified the functionality of the proposed control techniques.