Assessment Method of Wind Farm Harmonic Emission Level Based on Improved Covariance Characteristic of Random Vectors

The wind farm side harmonic impedance could not be neglected when assessing the wind farm harmonic emission level. Because of the low impedance characteristic of the wind turbine filter. This paper presents a new method to estimate the wind farm harmonic emission level at the point of common coupling (pee) based on improved covariance characteristic of random vectors. According to the topological structure of the wind farm, the equivalent harmonic impedance of the wind farm is calculated, with the measured data at pee the wind farm harmonic source is obtained. Since the system side harmonic source and wind farm side harmonic source are approximately independent, the background harmonic related term can be eliminated by using the covariance characteristic, then the system side harmonic impedance can be calculated. We can calculate the wind farm harmonic emission level. The harmonic impedances of wind turbines are aggregated to simplify the calculation of the wind farm side harmonic impedance. Based on the results of simulation and measured data, it verifies that the proposed method is effective to eliminate the background interference when evaluate wind farm harmonic emission level, and the proposed method is also effective when the background harmonic is large.