Implementation and experimental investigation of a sensorless field-oriented control scheme for permanent-magnet synchronous generators

Variable-speed wind energy conversion systems based on permanent-magnet synchronous generators (PMSGs) are typically controlled using the field-oriented control (FOC) principles. Therefore, accurate information of the rotor speed and position are essential to perform the required reference frame transformations. These signals can be obtained by mechanical sensors (e.g., position encoders or speed transducers) or via estimation schemes. This paper proposes a sensorless FOC strategy for direct-driven PMSGs in variable-speed wind turbines. A synchronously rotating reference frame phase-locked loop (PLL) that utilizes a model-based back elector-motive force (back-EMF) estimation is employed to estimate the rotor speed and position of the PMSG. The proposed sensorless FOC strategy is experimentally implemented, and its performance is investigated for all operation conditions and under parameter variations of the PMSG.