管路主動式噪音控制系統之理論分析與實務設計

Abstract

本論首先對管路主動式噪音控制系統進行理論分析.不同於一般 聲學模型的建立,本論文利用拉氏轉換(Laplace transform)得到的聲場轉 移函數建立系統方塊圖.所以適於以控制理論分析與探討.此一方塊圖中的 每個轉移函數在狀態空間的實現均為無限多維,故能完全反應聲場本身是 分散式參數系統(distributed-parameter system)的特性.本論文所處理 的系統架構屬於前饋式控制,前饋訊號來自上游的兩顆麥克風,透過DSP晶 片執行控制器,由一個控制喇叭送出控制訊號,所欲消除的噪音為寬頻的噪 音.透過系統方塊圖之分析,可得到在這樣的架構下,完全消音的控制器有 無限多組解,且可利用一個參數將其參數化,這些控制器具有簡單,與邊界 條件無關且在管路下游完全消音的優點. 本論文的其他部份以實 驗驗證上文所提的控制器,主要重點在喇叭與麥克風動態的判別與補償,使 用的方法包括離線設計與適應控制.離線的控制器設計對喇叭與麥克風的 動態不確定性十分敏感,而適應控制法則對此有較好的穩健性.實驗顯示這 樣的控制器的確具有有效消音的能力且與邊界無關的特性. Feedforward control methods of active noise cancellation system inducts are investigated both theoretically and experimentally. Without any modal truncation and thus reserving the distributed-parameter nature of theacoustic system, the plant model used in this thesis can completely characterizethe plan-wave behavior in finite-length ducts. A general noise cancellationframework is constructed for stability analysis and controlller synthesis.It is shown that there exist infinitely many controllers to perfectly blocknoise propagation toward downstream area. The most attractive features ofthese controllers are their simple structures and independency of boundaryconditions. One particular controller with special physical meaning isanalyzed and experimented. The experimental results show a consistent behavioras predicted by the theory. However, the performance of this controllerdegenerates due to the difference of sensors' dynamics and uncertainty of theplant. To alleviate this influence, an adaptive version of this controller isdesigned. Experimental results show that adaptive control is feasible andeffectively remedies these uncertainties.