Extended state observer based integral sliding model control for PMSG variable speed wind energy conversion system

In this paper, a novel extended state observer (ESO) based integral sliding model control (ISMC) approach is proposed to achieve maximum power point tracking (MPPT) for direct-driven permanent magnet synchronous generator (PMSG) variable speed wind energy conversion systems (VS-WECS). The proposed control approach adopts optimum tip speed ratio tracking scheme to realize maximum wind energy capture. Considering strong nonlinear and uncertainty features of VS-WECS, the ISMC is developed on the basis of the rotor angular speed tracking model. The sliding mode surface function consists of the integral term of the rotor angular speed tracking error, which ensures the rotor angular speed tracking without error at stable state. To eliminate the undesired chattering phenomena aroused from the sign function in the sliding mode control law, an ESO is designed to estimate the wind turbine aerodynamic torque. Using torque estimate feedback technique, the gain of sign function has the capability of self-adjustment according to the fluctuation of wind speed. Simulation results show that the proposed control approach has better tracking performance compared with that of conventional PI regulator.