Research On Improved DFT Harmonic Measurement Algorithms And Device Design

With the use of new energy,a large number of non-linear loads,distributed generation systems and impact loads are connected to the grid,which makes the existing grid structure appear highly electronic,and the resulting harmonic pollution problems can not be ignored.Accurate harmonic detection is the premise to deal with the harmonic pollution problem of power system,so it is particularly important to study it.Therefore,based on the research of existing grid harmonic measurement algorithms,the mainstream algorithm for determining grid harmonic measurement is DFT and its improved algorithm.Secondly,combined with the new characteristics of the current harmonic pollution problem of the power grid,there are three main aspects to analyze the shortcomings of the above methods:(1)The above methods are based on Fourier transform theory,through direct or indirect methods.The ideal harmonic detection accuracy is obtained under the condition when the sample data is large enough in the signal sampling process;(2)Due to the limitation of time resolution and frequency resolution,the local time-frequency variation characteristics of harmonics in power grid can not be described comprehensively;(3)The improved DFT algorithm has high computational complexity and low operability.In view of the above problems,the superiority of integrated compressed sensing technology in signal processing.This paper proposes a harmonic spectrum sensing measurement algorithm based on interpolation correction,which uses the grid harmonic signal model to derive the equality relationship under DFT transformation.Interpolation factor and spectral peak correction factor are used to establish a harmonic spectrum sensing matrix that conforms to the theoretical framework of compressed sensing.The sampled data is used as a priori information in the measurement process,and the reconstruction of harmonic spectrum information is realized according to the reconstruction recovery algorithm.The interpolation factor is used to solve the problem that the frequency resolution and the time resolution can not be simultaneously considered.The spectral peak correction factor is used to compensate for the non-integer deviation generated in the asynchronous sampling process,and the detection accuracy of the harmonic signal is ensured.At the same time,based on the problem of signal sparsity in the above measurement process,a harmonic spectrum sensing measurement algorithm based on windowed adaptive isproposed.The window function is excellent in sidelobe performance to reduce the grid signal in the DFT transform domain.The sparsity K,which simplifies the measurement process to reduce the sparseness of the grid fundamental-harmonic separation filter,optimizes the signal reconstruction and recovery algorithm,further improves the harmonic measurement accuracy and reduces the complexity of the algorithm implementation.Finally,a new type of power harmonic measurement device is designed according to the harmonic spectrum sensing measurement algorithm based on window adaptation.By setting up the test platform,the detection accuracy of the harmonic measurement device is verified according to the Class A measurement instrument standard.The accuracy,superiority and operability of the harmonic detection algorithm.