Direct Phase-Angle Detection for Three-Phase Inverters in Asymmetrical Power Grids

This article introduces a signal reformation-based direct phase-angle detection (DPD-SR) technique for three-phase inverters supporting asymmetrical grids. Asymmetries in three-phase systems may happen because of unbalanced three-phase loads, which can lead to the voltage asymmetry at the terminals of grid-tied inverters. The proposed DPD-SR technique can detect the voltage phase angle under asymmetrical conditions. The DPD-SR technique also offers precise and rapid phase-angle detection through signal reformation and trigonometric functions. In essence, the phase-angle detection is directly derived from the trigonometric properties of the line-line voltages, while signal reformation is implemented to handle asymmetrical voltages. The proposed method measures two line-line voltages and detects the phase angle of a three-phase system under both symmetrical and asymmetrical conditions. Unlike classical phase-locked loop (PLL) techniques, DPD-SR does not need any closed-loop proportional-integral (PI) controller, which significantly reduces the complexity and the delay in detecting the phase angle. In this article, the efficacy of the proposed technique is examined in comparison with the state-of-the-art PLLs under asymmetrical conditions through a set of laboratory experiments. The performance of the phase-angle detection is also tested as part of an inverter feeding an asymmetrical grid.