Enhanced method of rotor speed and position estimation of permanent magnet synchronous Machine based on stator SRF-PLL

Abstract

A stator flux oriented synchronous reference frame - phase locked loop (SRF-PLL) is proposed for the precise computation of rotor speed and position of permanent magnet synchronous machine (PMSM). A direct method of rotational speed computation based on the stator electromotive force (EMF) is initially formulated. Using the speed asa reference to the inverse Park and Clarke transformation blocks, the three-phase positive sequence stator flux is derived. A pre-stage low pass filter (LPF) is implemented to cancel out the ripples in the d-q components of the stator flux introduced by the dynamic operating conditions of inverter non-linearities and grid disturbances. The estimated three-phase positive sequence stator flux is used to compute the rotor position by aligning the total stator flux along the direct axis through a PLL block. Provision of the frequency amendment and ripple cancellation outside the PLL block results in a fast-dynamic response with an enhanced frequency adaptable capability. To validate the effectiveness of the proposed method, the sensorless vector control of grid integrated PMSM based wind-driven generator (WG) is analytically verified using the PSCAD/EMTDC simulation tool under various dynamic operating conditions such as wind speed variation and grid disturbances.