管道复合主动噪声控制系统及其实现

为了提高管道噪声主动控制系统的性能,设计出基于TI公司的TMS320C30芯片作为控制器的实时管道复合噪声主动控制系统(简称ANC系统)。针对前馈ANC可实现较宽的降噪频带,但在实际复杂系统中不能完全满足参考传感器信号和噪声声源要紧密相关要求;而反馈ANC系统中,降噪效果不依赖于声场的相关性,但其降噪频带较窄的特点,设计出复合FXLMSANC系统。在某风机、通风管路系统上进行ANC试验的结果表明,应用复合FXLMSANC方法,能获得比单独使用前馈FXLMSANC算法或反馈FXLMSANC算法更好的降噪效果。     

汽车多通道多频点自适应降噪方法研究

为了降低汽车驾驶室噪声、营造良好的驾驶和乘坐环境,提出了多通道多频点自适应降噪方法。分析了驾驶室噪声特征,建立了噪声频率与发动机转速关系模型;分析了单通道噪声主动控制方法,提出了自适应步长LMS算法,使收敛因子随噪声误差自适应变化,兼顾了算法收敛速度和稳态误差;以此为基础,设计了多通道多频点噪声主动控制方法。经仿真验证可以看出,自适应LMS算法不仅提高了算法收敛速度,而且降低了稳态误差;经驾驶室两通道降噪实验可以看出,多通道噪声主动控制技术可以实现驾驶室多区域降噪,通道一总声压级降低了4.3dB,通道二总声压级降低了9.8dB,充分证明了设计的多通道噪声主动控制方法的有效性。     

一种稳健的窄带反馈型主动噪声控制系统

传统窄带反馈型主动噪声控制系统采用并型自适应滤波器结构,用于合成参考信号时,仍存在参考信号合成质量较差、 滤波器权值的初值设置难度高、应对非平稳窄带噪声的能力不足等问题。 为解决以上问题,通过引入高效的串并型自适应滤波 器结构来合成参考信号,提出新型的窄带反馈型主动噪声控制系统,改善参考信号合成质量,进而提升系统的整体降噪性能。 新型系统不仅有效解决了传统系统存在的参考信号合成质量较差的问题,还降低了滤波器权值的初值设置复杂度,同时还提升 了系统应对非平稳窄带噪声的能力。 实验结果表明,新型系统较传统系统的前后两部分的降噪量分别提升了 7. 89 和 9. 18 dB。 仿真和实验结果共同验证了提出的系统较传统系统具有更强的稳健性和降噪性能。     

基于次级声源布局优化的主动降噪实验研究

提出了一种基于蒙特卡罗法声学仿真的次级声源布局优化方法,推导了多通道主动降噪(ANC)控制算法,搭建了双通道ANC实验系统,结合仿真结果和降噪实验研究了次级声源布局优化对ANC系统性能的影响。实验结果表明,对单频和混频噪声,次级声源布局优化后的ANC系统比未优化的ANC系统噪声主频抑制效果更显著,相同降噪效果下噪区域更广。该优化方法受条件限制较小,能够广泛应用于多种ANC系统。     

利用多层感知神经网络对空调噪声的控制研究

提出一种神经网络自适应噪声主动噪声控制(ANC)的方法。把后传播学习算法的多层感知神经网络用来对空调进行 ANC。对在三维空间传播的宽频带空调噪声 ,利用多层感知神经网络的 ANC获得了良好降噪效果。     

车内噪声主动控制系统鲁棒性分析与优化

针对多通道自适应陷波车内噪声主动控制系统存在的次级通路鲁棒性问题,首先,建立了系统的数学模型,定义评价系统降噪性能的收敛率和稳态误差增益;其次,结合理论推导、数值仿真和试验验证方法对系统次级通路鲁棒性问题进行深入分析,并推导了系统次级通路完全失配的边界条件,发现次级通路改变对系统稳态误差无影响,对系统收敛性的影响有正效...     

一种含次级通道在线辨识的窄带主动噪声控制系统

分析了噪声危害设备产生的谐波噪声,特别是以500 Hz或600 Hz以下的低频成分为对象,介绍了主动噪声控制(ANC)技术的原理、意义及发展现状。在实际声学场所,由于控制系统易受初级噪声功率、残余噪声幅值等因素影响而不稳定。在分析控制系统收敛条件的基础上,通过对系统误差引入一个比例因子从而改进系统模型,并以一维管道为实验平台,基于高速数字信号处理器(DSP)设计了含次级通道在线辨识的主动噪声控制器。实验结果表明,在250 Hz左右的频段上能够达到16 dB的降噪效果。     

基于分式函数的新变步长LMS算法

为了解决传统LMS算法在稳态误差和收敛速度之间的矛盾,提出了一种基于分式函数的新型变步长LMS算法(简称VXLMS算法)。因为新型变步长函数不包含指数运算,所以降低了运算量,加快了算法的收敛速度,同时也提高了数据跳变时的跟踪性能。在VXLMS算法收敛的条件下,通过理论推导确定了该变步长函数的参数取值范围,然后通过取不同参数值分析对算法性能的影响,选出最优参数值进行仿真分析。仿真结果表明:相同仿真条件下提出的VXLMS算法相对于VSSLMS算法和SVSLMS算法稳态误差更低、收敛速度更快,即说明提出的小计算量新变步长函数,通过调整步长因子使权向量快速达到最优,进而使VXLMS算法具有更好的收敛性、稳定性以及鲁棒性。     

改进的自适应算法在谐波检测中的应用

由于传统的最小均方(Least mean square LMS)算法收敛速度和稳态误差之间存在着不可调和的矛盾,而基于双曲正切函数的变步长LMS算法虽然有效的提高了收敛速度,但是其稳态误差较大,二者都只适用于高信噪比的环境。因此提出了改进的基于双曲正切函数的归一化最小均方算法。利用双曲正切函数和反馈误差的均值估计建立步长与误差之间的关系,控制权值及步长因子的更新,有效的降低了噪声的干扰,并在权值迭代的过程中引入了归一化算法,以使算法能适应大的动态输入范围,其次加入了动量因子,进一步提高算法的收敛速度。最后,在MATLAB/simulink仿真平台上搭建模型,仿真结果验证了算法在提高了收敛速度的同时,也有效的降低了稳态误差。     

改进LMS算法的仿真及其分析

在机械加工中,机械故障诊断的振动诊断技术在机械故障诊断学中占有重要地位.在振动信号处理方面,自适应信号处理是一个非常重要的分支,该方法能够有效的滤除含有背景噪声的信号,提取出有效的特征信号,但自适应算法有收敛速度与稳态误差之间的矛盾关系与步长因子易受噪声干扰等问题.为解决该问题,本文提出一种改进的变步长LMS算法:在算法中加入步长反馈因子,并对权值进行更新,使算法的收敛速度变快的同时保证了系统的稳定性,并加强了系统的跟踪能力.仿真结果表明:与其他算法相比,本文算法计算简单、收敛速度快、系统跟踪能力强,稳定性更好,能够有效的滤除噪声信号.     

Adaptive frequency tuner for active narrowband noise control systems

The reference frequency error can significantly degrade the performance of the narrowband active noise control (ANC) system. This paper investigates the relationship between the reference frequency error and the performance of the narrowband ANC system, and presents an adaptive frequency tuner which can reduce the reference frequency error and improve the performance of the system. Effectiveness of the adaptive frequency tuner is validated by simulation results using experimental transfer functions.     

IMPROVEMENT ON STABILITY OF ADAPTIVE NOISE CONTROL SYSTEM BY USE OF GRADIENT BACK-ADJUSTING FLMS ALGORITHM

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基于TMS320C6713的去噪自适应滤波器硬件实现

我们每天都会受到音频噪音的影响,原始信息会受到周围环境噪声信号的污染。为此,本文研究了一个多抽头自适应去噪实时硬件系统,它利用TMS320C6713上实现的最小均方算法（LMs）来去除与音频相关的应用程序中接收到的不期望出现的噪声信号。文章首先介绍了最小均方算法的c语言实现并在CodeComposerStudio上进行仿真,最后在C6713上实现。考虑不同的音频输入,进行了三项实验来测试所设计的自适应去噪系统的效率。实验采用300、500、800、1000和3000Hz的音频信号及男性语音信号为输入的参考信号,持续检测信号中的噪声,直至将它全部去除。此外,还研究了与自适应去噪系统性能相关的收敛速度、滤波器安排顺序以及信噪比。实验结果表明,所设计系统其信噪比有很大的改善。     

Quiet zone tuning in a non-ideal sound field

Most active noise control (ANC) systems are designed and analyzed in ideal sound fields, where ANC performances are predictable with acceptable accuracies. In many ANC applications sound fields are non-ideal with significant differences between real ANC performances and theoretical predictions. If one uses an ideal model to optimize locations of actuators or error sensors for an ANC system in a non-ideal sound field, the actual quiet zone is inevitably different from its theoretical prediction. It is desired that users of ANC systems can tune quiet zones by adjusting ANC configurations, such as locations of secondary sources or error sensors. Model-independent ANC (MIANC) systems are preferred for this purpose. In this study, a model-independent ANC system is improved, implemented and applied to create a quiet zone in a non-ideal sound field. Users of the system can adjust locations of actuators or error sensors to tradeoff between sizes of quiet zones and levels of noise attenuations. Experimental results are presented to demonstrate observations and effects of quiet zone tuning using the improved ANC system.     

一种新的LMS算法及其在明渠流量计中的应用

针对变步长LMS(least mean square)自适应滤波算法存在收敛速度慢和稳态误差比较大的问题,根据变步长滤波算法步长调整原理,提出了一种新的基于多项式的非线性变步长LMS算法,通过MATLAB仿真分析研究新算法中各参数对收敛速度和稳态误差的影响,并和已有的变步长LMS算法进行对比,结果表明该算法比已有的算法收敛速度快4倍,且稳态误差小。将新算法应用于明渠流量计回波信号的滤波处理,结果表明在低信噪比下,明渠流量计滤波性能良好,抗干扰能力强。     

Design of Time-Domain Equalizer in Elastic Wave Earth Channel

In low-frequency elastic wave through-the-earth communication system,because of multipath transmission caused by characteristics of the layered earth,the time domain equalizer is different from other wireless communication systems.A modified LMS algorithm of variable step size is proposed based on improvement of traditional LMS.On the base of principle and simulation analysis,the improved Least Mean Square(LMS)algorithm is analyzed and the performances are compared between the improved LMS algorithm and traditional LMS algorithm.In the improved algorithm,the contradiction between convergence speed and the steady-state error is considered at the same time.Therefore,the improved algorithm has good convergence properties and channel-tracking performance.     

Dynamic analysis of gear-rotor system with viscoelastic supports under residual shaft bow effect

This paper investigates the dynamic behaviors of a gear-rotor system with viscoelastic supports under effects of the gear eccentricity, the transmission error of gear mesh and the residual shaft bow. The investigated dynamic characteristics include system natural frequencies and steady-state response. The finite element method is used to model the system and Lagrangian approach is applied to derive the system equations of motion. The results show that the mass, the stiffness and the loss factor of the viscoelastic support will significantly affect system critical speeds and steady-state response. It needs larger loss factor and more rigid stiffness of the viscoelastic supports to suppress the systematic amplitude of resonance. As the results shown, the magnitude and phase angle of the residual bow have tremendous influence on first critical speed when the geared system mounted on stiff viscoelastic supports. The transmission error of the gear mesh is assumed to be sinusoidal with tooth passing frequency and it will induce multiple low resonant frequencies in the system response. It is observed that the excited critical speed equals to the original critical speed divided by gear tooth number.     

改进重复控制方法在并联型有源电力滤波器中的应用研究

有源电力滤波器的电流控制器设计直接影响电流谐波的补偿效果,采用比例积分PI控制跟踪交流信号时存在静差,而基于内模原理的重复控制在特定频率处有无穷大的增益,能够实现电流无静差跟踪,但系统动态响应速度慢。因此,该文提出将PI前馈控制与重复控制相结合的改进重复控制方法。该方法能够对电流进行无静差跟踪,且对系统谐波具有较好的抑制效果。通过Matlab/Simulink仿真软件和APF装置验证了系统对电流谐波具有较高的补偿精度且系统的动态性能较好。     

Modified-filtered-u LMS algorithm for active noise control and its application to a short acoustic duct

This paper presents a new adaptive algorithm for active noise control (ANC) that can be effectively applicable to a short acoustic duct, such as the intake system of an automobile engine, where the stability and fast convergence of the ANC system is particularly important. The new algorithm, called the modified-filtered-u LMS algorithm (MFU-LMS), is developed based on the recursive filtered-u LMS algorithm (FU-LMS) incorporating the simple hyper-stable adaptive recursive filter (SHARF) to ensure the control stability and the variable step size to enhance the convergence rate. The MFU-LMS algorithm is implemented by purely experimental ways, and is applied to active control of noise in a short acoustic duct, and is validated using two experimental cases of which the primary noise sources are a sinusoidal signal embedded in white noise and a chirp signal. The experimental results demonstrate that the proposed MFU-LMS algorithm gives a considerably better performance than other conventional algorithms, such as the filtered-x LMS (FX-LMS) and the FU-LMS algorithms.