Adaptive PLL for Frequency and Position Estimation of Electric Machines

This work proposes a new PLL (Phase-Locked-Loop) structure with adaptive filtering and control to improve frequency and phase estimation of Quasi-Type-1 Phase-Locked-Loops (QT1-PLL) for operation in conjunction with back-EMF estimators in position sensorless algorithms for the control of electric machines, as synchronous machines, specially permanent-magnet synchronous machines. An analysis of the structure and the limiting operating conditions of QT1-PLL and the proposed PLL is done. Experimental results are obtained, including unbalanced voltages, disturbances and voltage frequency variation, typically presented in variable speed electric machine systems. The obtained results show that the proposed structure significantly improves the sensibility of the PLL due to unbalanced voltages, achieving steady zero error due to ramp input frequency and phase, capable of operating in a wide input frequency range.