| With the rapid development of the power electronic technology, various power electronic devices and nonlinear elements, especially of many kinds of rectifier and switcher, were applied widely in power system. Damages resulted from harmonic become more and more serious. People pay more and more attention to harmonic online detecting and control. Based on the condition of 300KA aluminum electrolyzation rectifying electric network, the character of harmonic and the chief methods of detecting harmonic, and the whole design of harmonic online detection system are roundly introduced in this paper, which laid the foundation for harmonic suppression in aluminum electrolyzation rectifying electric network.The present condition, the character, the cause and main harm of harmonic are introduced in this paper. The primary electronic devices which bring more effect in harmonic pollution are elaborated. In order to reduce the harm of harmonic problem, harmonic suppression is necessary. But the premise of harmonic control is that the harmonics parameters can be accurately and real-time detected. Then the chief harmonic detection methods are analyzed in this paper, including FFT, instantaneous reactive power, wavelet analysis and adaptive filter and so on. Comparing the advantages and disadvantages of those harmonic detecting methods and analyzing harmonic character in aluminum electrolyzation rectifying electric network, a new method based on variable step size adaptive filter algorithm to solve the drawbacks of traditional LMS, such as, the speed and precision of algorithm convergence can be seriously affected by SNR, is presented. At the same time, the inherent time delay of digital filtering can be solved by the predictive function of adaptive filter. Simulation and experiment results prove the validity of the method in electric harmonic detection.Base on the modified adaptive filter algorithm, a new harmonic online detection system is presented, which includes the design scheme of system hardware and software. The design method of system circuit module and software function module, which include harmonic detection module and data communication module and so on, is presented. The practical effect applied to project proves that this detecting system can accurately detect the magnitude of each harmonic element, and transmit the detection data to the users interface, and then supply the evidence for workers to compensate and control harmonic in aluminum electrolyzation rectifying electric network. |
