Research And Application Of Active Noise Control System In Vehicles

The ever growing demand for comfortable car ride,the internal noise of the car has become an important issue in the development of the modern automobile industry.Many traditional passive noise reduction techniques have been reported in the literature to suppress the effect low and high frequency noise in the cars.However,these approaches are somehow limited to their performance and have minimal effect at the low frequencies.As internal car noise lies at the low frequencies,ANC(active noise control)technology inside the vehicles has become a promising solution with better low frequency noise control performance.However,at present,domestic research on ANC(Active Noise Control)system for interior noise is in the stage of simulation and experimental phase.There are many uncertain parameters for the improvement of some algorithms,which is difficult to implement in practical applications.In order to improve the processing performance and noise reduction effect of the ANC system inside the vehicle,this paper focuses on the control structure and algorithm of ANC system.Aiming at the mutual constraint between the convergence speed and steady-state error of the algorithm,an effective variable step size algorithm is proposed and verified by simulation.Finally,Conduct actual experiments.The secondary noise of the LMS algorithm is directly superimposed with the primary noise and is acquired by the error sensor without considering the influence of the secondary path on the system.However,in practical applications the secondary noise cannot be directly acquired by the error sensor.It must be superimposed with the primary noise after passing through the secondary path.While,the phase of the primary noise and the secondary noise do not correspond well,which seriously affects the actual situation of Noise reduction effect.Focusing at this problem,the filtering-X LMS algorithm is deeply studied.Compared with the LMS algorithm,the FXLMS algorithm introduces the influence of the secondary path and uses the offline secondary path modeling method to estimate the secondary path which improves the ANC system in practice.Single channel noise reduction scope of ANC system is limited,should not be used for the three-dimensional space of noise suppression,yet the internal environment is similar to a closed three-dimensional space,multi-channel control algorithm is adopted in this project.In order to simplify the calculation of the algorithm and improve the noise in the practical application of ANC system tracking ability,optimize the multi-channel control algorithm,two channel control algorithm,effectively reduce the amount of calculation of the algorithm.The adaptive algorithm for the system has the problems of fast convergence,large steady-state error,small steady-state error and slow convergence.In this thesis,the variable-step NFXLMS algorithm is studied in detail and the function relationship between iteration number and step size is introduced.The simulation analysis shows the improved variable step size NFXLMS algorithm has faster convergence speed and lower steady-state error than the traditional FXLMS algorithm and the modified variable step size NFXLMS algorithm.Finally,the improved algorithm is applied in the multi-channel active noise control system and the actual experiment is carried out for the car noise.The new algorithm achieves faster convergence speed and better noise reduction effect over traditional approaches.