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

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 as a 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.