Stator-flux-oriented sliding mode controller for DFIG with variable hysteresis loop for limiting switch frequency of rotor-side power converter

Abstract

Doubly fed induction generator (DFIG) is the most implemented electric machine in wind energy conversion systems (WECS) due to reduced size converter, active and reactive power control and economic factors. However, the power electronic stage needs an accurate controller that allows to follow the stator power regulation. As a result, Sliding-Mode Control (SMC) has been successfully implemented in DFIG because the natural discontinuous control signals arising from the controller can be used for direct switching of power electronic devices. Yet, switching frequency of SMC depends on the sample rate, controller parameters and electric machine dynamics; this conditions produce a control signal with a variable switching frequency hindering implementation. In this paper a stator-flux-Oriented sliding-mode controller with a hysteresis band that limits the switching frequency of power electronic devices to a set value is presented. This methodology improves previous proposals by limiting switching frequency making implementation more feasible. Simulation results are presented to validate the control methodology.