Research On Modal Decomposition Method And CPT In Harmonic Interharmonic Detection

With the rapid development of smart grid,more and more new energy generation devices and nonlinear loads are connected to the grid.As a result,the problem of power quality in power system becomes more and more serious.Therefore,fast and accurate detection of harmonic and interharmonic are the premise of harmonic control.The detection accuracy and real-time measurement of harmonic interharmonic are considered simultaneously in this paper.1)In terms of detection accuracy,the paper analyzes and researches the detection method based on the Variational Mode Decomposition(VMD)for noise problem.Subsequently,it is found that the VMD algorithm cannot accurately detect the harmonic and interharmonic of dense frequency.In view of the problem of dense frequency,it further studys the detection method based on the Analytical Mode Decomposition(AMD);2)In the aspect of real-time engineering application,the method of harmonic and interharmonic current detection based on the improved Conservative Power Theory(CPT)is mainly studied.Firstly,a method based on Variational Mode Decomposition(VMD)and Teager energy operator is proposed to detect harmonic and interharmonic in low signal-noise-ratio signals.The correlation coefficient method is used to optimize the VMD algorithm,then the signal is decomposed using the VMD algorithm,and then the decomposed continuous and intermittent harmonic intrinsic mode function components are demodulated using the teager energy operator.The simulation results show that the proposed method can effectively separate the continuous and intermittent harmonic signals with low SNR.At the same time,it has higher detection accuracy and better noise robustness.Secondly,because the VMD cannot accurately decompose the harmonic and interharmonic among the dense frequency harmonics in the signal.A detection method combining all-phase Fast Fourier Transform(ap FFT)and Analytical Mode Decomposition(AMD)is further proposed to solve the problem of dense frequency.For signals with dense frequency components,the ap FFT phase spectrum flatness is used to identify the dense frequency,and the optimal binary frequency is obtained by using quantum particle swarm optimization.According to the obtained binary frequency,the AMD is used to analyze the harmonic signal.The experimental results show that the proposed method is effective andaccurate for the detection of dense frequency signals.Finally,aiming at the problem of real-time measurement of harmonic and interharmonic current detection,the proposed CPT is applied to the measurement of harmonic and interharmonic current.The basic principle of CPT is analyzed and studied,and a simulation model is established.Based on this model,the detection accuracy and dynamic characteristics of ip-iq method and CPT are analyzed and compared in the case that the power grid voltage does not contain harmonics.The CPT is verified by DSP experiment.According to the principle of CPT detection,the CPT is affected by voltage distortion in the process of detecting harmonic current.So the extraction of positive fundamental wave sequence is adopted to improve CPT.The simulation results show that the enhanced method also has high detection accuracy with the distorted voltage.