Optimum control strategies in energy conversion of PMSG wind turbine system without mechanical sensors

The amount of energy obtained from a wind energy conversion system (WECS) depends not only on the characteristics of the wind regime at the site, but it also depends on the control strategy used for the WECS. In order to determine the gain in energy derived from one concept as compared against another, models of several autonomous WECS have been developed using Matlab Simulink software. These allow easy performance evaluations and comparisons on different control strategies used, and determine the amount of energy injected to the grid in the case of the grid-connected systems. This paper also proposes a prototype version of the control strategy of a 20-kW permanent-magnet synchronous generator (PMSG) for maximum power tracking and compares with the results produced by previous strategies. Advantages of this mechanical sensorless control strategy for maximum power estimation are demonstrated by digital simulation of the system.

I. Introduction

Optimum wind energy extraction is achieved by running the wind turbine generator (WTG) in variable-speed variable-frequency mode. The rotor speed is allowed to vary in sympathy with the wind speed by maintaining the tip speed ratio to the value that maximizes aerodynamic efficiency. In order to achieve this ratio, the permanent-magnet synchronous generator (PMSG) load line should be matched very closely to the maximum power line of the wind turbine generator. In such a case, a good matching exists between the generator and the load for the best performance of the system, as well as the maximum utilization of the wind driven PMSG. However, the recent advancements in power electronics and control strategies have made it possible to regulate the voltage of the PMSG in many different ways. When the generator torque line can be controlled, the generator loading of the turbine can be made to follow the desired locus such as the optimum shaft power locus.