Variable gradient-based phase locked loop for accurate frequency estimation of distorted grids

Area of Science:

• Electrical Engineering
• Control Systems
• Power Systems

Background:

• Synchronous Reference Frame Phase Locked Loops (SRF-PLL) exhibit limitations in accurately estimating grid frequency under harmonic disturbances.
• The large-signal model reveals poor filtering performance of SRF-PLLs when subjected to grid distortions.

Purpose of the Study:

• To develop an improved phase locked loop (PLL) for accurate grid frequency estimation in the presence of distortions.
• To introduce a Variable Gradient-based Phase Locked Loop (VG-PLL) that enhances filtering capabilities.

Main Methods:

• Establishment of a large-signal model for the SRF-PLL under harmonic disturbances.
• Development of a VG-PLL utilizing the variable gradient method.
• Application of a Lyapunov function to prove the input-state stability of the VG-PLL.

Main Results:

• The developed large-signal model confirmed the SRF-PLL's inadequate filtering for frequency estimation in distorted grids.
• The VG-PLL demonstrated enhanced filtering capabilities compared to the SRF-PLL.
• Input-state stability of the VG-PLL was mathematically proven using a Lyapunov function, even under grid distortions.

Conclusions:

• The proposed VG-PLL offers a significant improvement over the SRF-PLL for frequency estimation in distorted power grids.
• Experimental validation confirmed the superior performance and accuracy of the VG-PLL under various grid distortion scenarios.