Application Of Improved Nonstationary Harmonic Detection Algorithms And Compound Control Strategy In APF

As a new type of harmonic suppression device,APF can quickly and flexibly eliminate the harm brought by harmonic in power network,and has been widely concerned and applied at home and abroad.At present,scholars all over the world focus on the harmonic detection algorithm and related control strategy.In terms of detection algorithm,as a result of the power electronic technology innovation and the rapid development of smart grid,all kinds of nonlinear devices and loads are widely distributed in the power system of power generation,transmission and distribution,power link,in the current power grid harmonic are mainly composed of non-stationary harmonic signals with noise,the traditional harmonic detection algorithm can not meet the current needs.In terms of control strategy,APF should have strong robustness while ensuring that it can track the instruction signal accurately and quickly.Firstly,this paper summarizes the development status and research focus of APF in China,elaborates on the harmonic detection technology and control strategy of APF,and determines the research direction of the subject.Secondly,the single-phase low-voltage vsi-lcl APF is taken as the research object,and the harmonic detection technology and control strategy in APF are studied respectively.The non-stationary harmonic detection technology and the repetitive h-infinity composite control strategy are combined to form the entire APF control system,so as to achieve fast and accurate output compensation current and reduce the harmonic content of the power grid.In the link of harmonic detection,this paper proposes a pe-ceemd decomposition method based on PE algorithm to improve the unsatisfactory performance of overall empirical mode decomposition(CEEMD)to improve the phenomenon of mode aliasing and generate false components.Considering the problem of noise residue in decomposition,a new wavelet threshold denoising(WTD)method under the threshold function is adopted to de-noising the decomposed IMFS,and then feature extraction of the processed IMFS containing harmonic component information is carried out.In control links,this paper proposes a repeat-h-infinity compound control strategy,the repetitive control delay link as a system of external disturbance,the mathematical model is constructed based on the repetitive controller and the APF of generalized state space expression of the solving process of compensation in the repetitive control loop into a standard h-infinity of a class of linear systems,linear matrix inequality(LMI)method is used to design the optimal h-infinity controller,avoid the traditional repetitive control stability compensator to solve the difficult problem.In order to verify the effectiveness and feasibility of the harmonic detection algorithm and control strategy proposed in this paper,a new WTD harmonic detection program under pe-ceemd was designed using Matlab/Simulink software,and an APF simulation platform based on repetitive h-infinity control was built.Simulation experiments were conducted under various working conditions.Harmonic detection simulation experimental results show that the proposed algorithm is effective to improve the traditional modal aliasing and false weight in the algorithm,and hybrid control strategy is to avoid the traditional repetitive control stability compensator to solve difficult problems,compared with traditional repetitive control strategy can effectively improve the dynamic and static quality of APF and robustness.