Research On Power System Harmonic Detection And Suppression Methods

In recent years, harmonic contamination become increasingly serious with the extensive use of non-linear loads, it is a serious threat to security and stability of the power system and electrical equipment. In order to control the harmonic pollution effectively, harmonic current detection technology and suppression techniques become more widespread attention.Firstly, the background and significance of the research, and the research status of the harmonic current detection methods, and the harmonic suppression methods are described in this paper; the power quality's basic concepts, affecting factors, classification and main parameters are given; the causes of harmonic, and the concepts and the theoretical foundation of harmonic are expounded in detail; the harmonic's harm to power system and the limits of harmonic in the utility grid are elaborated.Secondly, the three typical harmonic current detection methods are researched, and the three harmonic current methods's performance are simulated and analyzed. Focus on the adaptive harmonic current detection method, found that the traditional adaptive harmonic current detection method's feedback signal does not directly reflect the situation that the adaptive filter track the target signal, and that is one of the reason to reduce the convergence rate and the steady-state accuracy of the algorithm. To overcome this shortcoming of the conventional adaptive algorithm, the way how to extract the true error that can reflect the situation that the adaptive filter track the target signal will described in detail, take the true error as the feedback signal in improved adaptive algorithm, a new harmonic detection method based on LMS algorithm of improved adaptive gain is proposed. Compare the simulation results of the improved LMS algorithm in fixed step with the simulation results of the traditional LMS algorithm in fixed step by MATLAB, and prove the superiority of improved algorithm. In addition, take the improve-algorithm's feedback as the argument of sine function to control updating of the step size, enhancements, proposes a new variable step size LMS algorithm, and compare the simulation results of the improved LMS algorithm in fixed step with the simulation results of the new variable step size LMS algorithm, and analyze the simulation results.Thirdly, the harmonic suppression methods are researched. Focus on researching the active power filter's working principle, mathematical model and the designing methods of the main circuit parameters. Two of control track methods of active power filter are compared in this paper, and the hysteresis control method is chosen as the control method for APF.Finally, the way that how to apply the single-phase improved algorithm to the three-phase system is introduced, and a closed loop system's structure of APF is provided, and in this system the improved algorithm is taken as detection method, and the hysteresis comparator is taken as control method. The model of closed-loop system is built in the Matlab/Simulink, and some sub-modules is given and analyzed, simulation results are given and analyzed and summarized; the program flow of the improved algorithm to calculate harmonic current is given.