Maximum Electrical Energy Production of a Variable Speed Wind Energy Conversion System

This paper proposes a control strategy for Wind Energy Conversion Systems (WECSs) aiming in both maximum power harvesting from the wind turbine and minimum power loss of the electrical generator. Thus, maximum efficiency along the whole wind energy conversion process is achieved and additionally expansion of the exploitable wind speed region towards the lower-speed range is accomplished. A squirrel cage induction generator connected to the power grid by means of two back-to-back converters is used. Field oriented control is applied and a system of two Search Controllers (SCs) is introduced for the control of the d- and q-axis stator current components of the generator. The maximum power at the wind turbine is achieved through the one SC by adjusting the q-axis current and through this, the generator speed. Another SC is introduced in order to maximize the efficiency of the electrical generator by controlling its flux-linkage. The dynamic performance of the system is improved by introducing control loops that compensate the delayed response of the flux-linkage to the d-axis current component and provide improved torque control operation. Several experimental results are presented to demonstrate the effectiveness and operational improvements of the proposed control system.