EPLL-Based Speed Estimation: An Option for High-Performance Sensorless Induction Motor Drives

The growing need to improve system reliability while reducing costs in induction motor (IM) drive systems has become a primary driving factor behind the advancement of high-performance sensorless control (SC). In this paper, an enhanced phase locked-loop (EPLL)-based speed estimation scheme is thus proposed, which offers an alternative for speed-sensorless direct torque control (DTC) of IM drives. The EPLL is accepted as a popular synchronization technique in single-phase applications, and this paper extends this approach to IM drives for the purpose of speed estimation. In this scheme, the estimated speed is obtained from three-phase stator currents through the EPLL, thereby minimizing the reliance on motor parameters and enhancing robustness against motor parameter variations. However, various harmonics appearing in the stator currents may challenge the estimation. Accordingly, the EPLL scheme exploits the pre-filter to address this issue. Furthermore, an amplitude normalization method is applied subsequent to the pre-filter stage, enabling to avoid the amplitude mismatch. Simulations are conducted to validate the estimation performance of the EPLL scheme under different cases. Also, the results are compared with those of the conventional synchronous reference frame PLL (SRF-PLL) scheme.