Design and Operation of a Phase-Locked Loop with Kalman Estimator-Based Filter for Single-Phase Applications

This paper describes the design procedure of a phase-locked loop (PLL) preceded by a Kalman estimator-based filter. It provides a highly accurate and fast estimate of the grid frequency and phase angle in grid-connected power electronic applications. Moreover, it enables the transformation to the rotational dq frame for various control purposes. Closed-form equations allow for a performance driven design for both PLL and estimator. By using a variable sample frequency controlled by the PLL, the Kalman filter is always operated around its center frequency, which is the rated grid frequency. The new topology is compared to other published single-phase PLL designs and its operation is verified by both simulations and experiments. The PLL exhibits excellent performance even under severely distorted utility grid voltage conditions. This robustness makes it very suitable for use in systems connected to grids having an important share of non-linear loads