Robust Synchronous Reference Frame Phase-Looked Loop (PLL) with Feed-Forward Frequency Estimation
This work provides an incremental improvement in the robustness and tracking performance of SRF-PLLs, which are crucial for power system interfacing and control applications.
This paper presents a robust synchronous reference frame phase-locked loop (SRF-PLL) design that maximizes the phase margin and uses a normalization scheme to make the loop insensitive to input amplitude variations. The key improvement is achieved through a robust, model-free feed-forward frequency estimator, which enhances transient behavior and tracking of frequency ramps, especially with noisy and time-varying harmonic signals.
Synchronous reference frame phase-locked loop (SRF-PLL) techniques are widely used for interfacing and control applications in the power systems and energy conversion at large. Since a PLL system synchronizes its output with an exogenous harmonic signal, often 3-phases voltage or current, the locking of the frequency and phase angle depends on the performance of the feedback loop with at least two integrator terms, and on the distortions of the measured input quantities. For the conventional SRF-PLL with a proportional-integral (PI) control in feedback, we are providing a robust design which maximizes the phase margin and uses the normalization scheme for yielding the loop insensitive to the input amplitude variations. The main improvement in the transient behavior and also in tracking of frequency ramps is achieved by using the robust feed-forward frequency estimator, which is model-free and suitable for the noisy and time-varying harmonic signals. The proposed feed-forward-feedback SRF-PLL scheme is experimentally evaluated on the 3-phases harmonic currents from a standard PMSM drive with the varying angular speeds and loads. Both, the tracked angular frequency and locked phase angle are assessed as performance indicators of the proposed SRF-PLL with feedforwarding.