Abstract
A new method is proposed for obtaining the maximum power output of a doubly-fed induction generator (DFIG) wind turbine to control the rotor- and grid-side converters. The efficiency of maximum power point tracking that is obtained by the proposed method is theoretically guaranteed under assumptions that represent physical conditions. Several control parameters may be adjusted to ensure the quality of control performance. In particular, a DFIG state-space model and a control technique based on the Lyapunov function are adopted to derive the control method. The effectiveness of the proposed method is verified via numerical simulations of a 1.5-MW DFIG wind turbine using MATLAB/Simulink. The simulation results show that when the proposed method is used, the wind turbine is capable of properly tracking the optimal operation point; furthermore, the generator’s available energy output is higher when the proposed method is used than it is when the conventional method is used instead.
Highlights
Generator wind turbines are divided into two groups: fixed-speed wind turbines (FSWT) and variable-speed wind turbines (VSWT)
Since VSWTs operate at variable rotor speeds, the generator is often connected to the grid via a converter system for synchronization [2,3]
For VSWTs based on synchronous generators (SG), permanent magnetic synchronous generators (PMSG) or squirrel-cage induction generator (SCIG), a full converter must be installed [2]; for VSWTs that use a doubly-fed induction generator (DFIG), a partial converter must be installed at the rotor side [3]
Summary
Generator wind turbines are divided into two groups: fixed-speed wind turbines (FSWT) and variable-speed wind turbines (VSWT). Other methods that do not use an anemometer, such as the MPPT-curve method [8,9] and perturbation and observation (P&O) [4], cannot track the maximum power point either exactly or quickly, because they operate basically on the generator’s output Such methods are mainly applied either to photovoltaic power systems where the inertia of the generator is zero or to PMSG wind turbines with a DC/DC converter [2,4]. The MPPT-curve method indexes the current rotor speed (or power output), as well as the wind turbine’s MPPT curve to determine a reference power output (or rotor speed) [8,9] It does not require any perturbation signal and is robust; this method cannot track the maximum point quickly because of the high inertia of the generator wind turbine system. Simulation results will be evaluated and compared to the results of a wind turbine using the conventional MPPT-curve method with PI controllers
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