Harmonics detection based on dual observer method for distorted grid

In this paper, a harmonics detection method based on robust frequency extraction observer and Luenburger observer is proposed. In detail, a robust observer is first used to extract real time frequency of grid currents. Then by zero-crossing detection method we design, the grid frequency is converted to phase. After that, a Luenburger observer is established using phase and integrated current signal as input, proved effective by Lyapunov function and LaSalle’s Invariance Principle. In the end, the observer realizes the harmonics detection by giving harmonics component of each order. The simulation results show that the proposed method has the advantages of fast dynamics, strong robustness, high accuracy and anti-noise, which can deal with the distortion of the power grid and the sudden change of frequency.