Sensorless control of PMSG in variable speed wind energy conversion systems

A sensorless control strategy for a permanent magnet synchronous generator (PMSG) in variable speed wind energy conversion system (WECS) is proposed. The proposed method is based on recursive least square estimation (RLSE) algorithm for rotor speed estimation using an equation containing only stator flux and current. Further, rotor position information used for coordinate transformation is computed using the estimated speed. Stator flux required for speed estimation is obtained using a programmable low pass filter (PLPF). The estimated speed is used as the feedback signal for the speed control loop of the vector controlled machine side converter control system whose command speed is obtained from a wind speed sensorless maximum power point tracking (MPPT) controller. The front end converter is vector controlled in grid voltage reference frame. Simulation is carried out in order to verify the proposed algorithm.

I. Introduction

Variable speed WECS in comparison to fixed speed ones have many advantages such as improved energy capture, better power quality, reduced mechanical stress and aerodynamic noise [1]. These systems can be controlled in order to enable the turbine to operate at its maximum power coefficient over a wide range of wind speeds, obtaining a larger energy capture from the wind [2]–[4]. However, speed up gear in conventional variable speed WECS increases the maintenance requirements in addition to making the system bulky; moreover, torque surges due to sudden wind gust may cause its breakdown. Therefore, direct drive (DD) WECS are becoming favoured ones. They have reduced overall size, lower maintenance cost in addition to having higher overall efficiency and reliability [5]–[7]. Presently, most of the direct drive WECS use electrically excited synchronous generators. However, PMSG is favoured more and more in developing new designs because of higher efficiency, high power densities, availability of high-energy permanent magnet material at reasonable price, and possibility of smaller turbine diameter [7]–[8].