Self-synchronising stator terminal control of permanent magnet synchronous generators for wind energy conversion systems

Abstract

Conventional wind energy conversion systems (WECS) typically employ rotor side synchronous frame current control strategies to regulate the active/reactive power supplied by the WECS generator. Such strategies require accurate information regarding the rotor position and speed in order to set the dq frame reference currents and to perform the necessary frame transformations. This information can be obtained using a rotor speed sensor (i.e. a shaft encoder) or via a sensor-less strategy in which a dynamic machine model and stator current measurements are used to estimate the true rotor position. This paper now presents an alternative approach to control the active/reactive power supplied by the WECS permanent magnet synchronous generator (PMSG). The proposed strategy uses the three phase converter modulation commands to identify the phase and frequency of the PMSG stator terminal voltages. This enables the direct regulation of the real and reactive power extracted at the PMSG terminal voltages using a stationary frame Proportional + Resonant (PR) stator current regulation strategy, without requiring precise knowledge of the rotor position. Maximum power point tracking (MPPT) functions are realized using the measured PMSG terminal voltage frequency to form an estimate of the rotor speed. The result is a simple robust WECS control strategy that rapidly and accurately tracks rotor speed changes caused by wind speed variations. Detailed simulation and experimental results obtained for a scaled laboratory prototype system are presented to validate the proposed strategy.