Comparison of Control Strategies for Squirrel-Cage Induction Generator-Based Wind Energy Conversion Systems
Direct Torque Control, Field Oriented Control, Flux Slip Control, Squirrel Cage Induction Generator, Wind Energy.
The squirrel cage induction generator is a robust and low cost alternative to variable speed wind energy conversion systems. For this type of generator, direct torque control, direct stator-field-oriented control, direct rotor-field-oriented control, stator-flux slip control and rotor-flux slip control can be used for maximum power point tracking. Stator-flux slip control and direct torque control have simple schemes with fast dynamic responses, since they do not have internal current controllers. However, stator-flux slip control presents high inrush-current and a poor dynamic response and direct torque control presents high torque ripples and poor performance at low speeds. On the other hand, rotor-flux slip control, direct stator-field-oriented control and direct rotor-field-oriented control have fast dynamic response, low inrush current and low error at maximum power point tracking, but have current controllers and offer a larger complexity in the control design. The objective of this work is to define the most suitable control strategy by evaluating the following performance indexes simultaneously: maximum power point tracking, total harmonic distortion, inrush current and dynamic response. Simulations are performed in order to analyze the performance of the control strategies. Tests were carried out for the five control strategies and the direct rotor-field-oriented control presented the best trade off considering maximum power point tracking, total harmonic distortion and dynamic performance, despite it does not have the best inrush current.