Steady-State Linear Kalman Filter-Based PLLs for Power Applications: A Second Look

In three-phase power and energy applications, the synchronous reference frame phase-locked loop (SRF-PLL) is a popular tool for synchronization purposes. The SRF-PLL can be easily and effectively customized for different scenarios by changing its loop filter. Recently, some supposedly different PLLs using the steady-state linear Kalman filter have been developed. The main aim of this letter is to analyze these PLLs. It is demonstrated that they are actually equivalent to some well-known SRF-PLL structures and, therefore, provide no advantage compared to them.