Dual Phase-Locked Loop-Based Speed Estimation Scheme for Sensorless Vector Control of Linear Induction Motor Drives

In power electronics and power systems, the dual-phase-locked loop (DPLL) is a well-accepted approach to maintain zero steady-state errors when subjecting to a frequency ramp input. This distinctive characteristic of the DPLL may make it as a promising candidate for speed estimation in speed-sensorless drive systems. Considering this issue, a DPLL-based speed estimation scheme for linear induction motor speed-sensorless drive systems is presented in this article to achieve accurate speed estimation. The basics of the DPLL and the direct application of the DPLL scheme are provided. However, in practice, the direct application of the DPLL scheme may degrade the performance of the entire system, which includes the nonidealities in the secondary electromotive force (EMF) signals, such as harmonics and parameter variations. Accordingly, the prefilter and the amplitude normalization scheme are employed to mitigate the effect of nonidealities. Meanwhile, the small-signal model of the proposed DPLL scheme is presented, enabling the analysis of the dynamic performance and the comparison of the synchronous reference frame phase locked-loop scheme. In addition, a parameter tuning guideline of the proposed DPLL scheme is detailed by using the derived small signal model. The performance of the proposed DPLL scheme is investigated by experimental tests.