| In recent years,as people required to improve the living environment,the noise problem has attracted more and more attention.The traditional passive noise reduction method can get better noise control effect,but it also has some disadvantages such as high cost and poor adaptability to the environment.The active noise control(ANC)system which is based on adaptive control theory can not only optimize its own system in real-time,but also can effectively control the low frequency noise which is difficult to be processed by the passive mode.But the most existing ANC researches is based on the Gauss distribution with steady noise,little research on impulsive and/or impact noise.In fact,because of its high energy random noise,the common ANC system is difficult to achieve effective effect.Therefore,aiming at the above problems,this paper takes the general cooling axial fan as the research object,based on the improved Fx NLMS algorithm,and improves the performance of the ANC system.In view of the above description,the main work of this paper includes the following aspects:1)In order to ensure the accurate realization of the ANC system,the hardware platform design of ANC system is completed.Firstly,according to the noise mechanism and characteristic of the experimental axial flow fan this paper design the hardware structure of the ANC system in detail,including system structure,the hardware structure of controller,the duct acoustic and electroacoustic system.2)Two factors affecting the noise reduction effect of ANC system(secondary channel identification and adaptive algorithm)are studied in detail,and a method to improve the performance for anti interference capability of the system is proposed.In this paper the convergence characteristics of FXNLMS algorithm and FXLMS algorithm are analyzed in detail based on adaptive control principle,and using the Simulink to found the anti pulse of performance problems of these traditional algorithms.Finally adding the threshold method to improve Fx NMS algorithm have been proposed and proved its feasibility through simulation.3)Implementation of ANC system based on the DSP DM642.The audio module and the software realization of data transfer channel,which are for the designed hardware platform and the ANC system control structure,have carried on the detailed analysis.And in order to improve the operation speed of the system,the feasibility of floating point operation is studied,and the implementation process of the control algorithm is completed.4)Completing the experimental test and results analysis of the proposed ANC system.For the proposed ANC system,the design of the experimental scheme,the threshold selection and the secondary channel identification are completed in this paper,and a number of experiments are carried out for the fan noise with impulsive noise.The experimental results show that the proposed method in this paper can effectively improve the ANC system of anti impulse interference noise performance.For the fan noise mixed with impulse noise,the proposed ANC system not only can achieve nearly 10 d B on the rotational noise(near 220 hz and 440hz),but also can reach average 5d B on the broadband noise between 100-300 Hz.This shows that this method can improve the convergence rate of the system to a certain extent,and also improve the overall performance of the system. |
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