One-Step-Prediction Discrete Observer Based Frequency-Locked-Loop Technique for Three-Phase System

Abstract

In grid-tied power converters, the grid parameters such as the frequency, phase angle of the fundamental component, and the harmonics are essential to the control of power converters, the fast and accurate estimation of the grid parameters is a challenge especially for high-order harmonics. This paper proposes a one-step-prediction (OSP) discrete observer (OSPDO) to observe the fundamental and harmonic sequence components of the grid voltage. Based on the proposed OSPDO, a frequency locked loop (FLL) is designed. The proposed OSPDO-FLL has a good robustness to sampling frequency on dynamic response and high precision for frequency estimation. The proposed algorithm can estimate up to maximum 50th harmonic with a low sampling frequency thanks to the robust properties. Finally, the good characteristics of the proposed synchronization algorithm are verified by simulations and laboratory experiments.

Nonlinear Self-Synchronizing Current Control for Grid-Connected Photovoltaic Inverters

“…Moreover, adding a PLL loop to the main control loop will add more complexity to the system [16]. Many approaches have been proposed in the literature to improving the performance of the PLL schemes to address any potential instability issues resulting from the interaction between the PLL schemes and current control loop [17,18]. These challenges have motivated researchers to develop control schemes for grid-connected inverters that do not require a synchronization system such as PLLs [19][20][21][22].…”