效率最佳化之單相無刷直流風扇馬達使用霍爾感測器或無感測控制

Abstract

本論文實現效率最佳化之單相無刷直流風扇馬達使用霍爾感測器或無感測控制策略。本文提出簡單的模型方法並配合適當的參數鑑別，建立符合單相無刷直流風扇馬達特性的數學模型，其非線性的轉子磁通量分布特色是利用建表的方式來代表。經由電腦模擬與實際量測結果比對後，可驗證該模型的準確性。本文比較不同的控制策略，包含開迴路硬換相電壓模式控制、開迴路軟換相電壓模式控制以及閉迴路電流模式控制，分析其電流波形以及運轉效率的優劣。本文結合閉迴路電流模式控制以及開迴路軟換相電壓模式控制的優點，配合霍爾感測器輸出訊號的回授，可使單相無刷直流風扇馬達在廣泛的速度範圍內達到效率最佳化。本論文亦實現高效率且低成本的單相無刷直流風扇馬達無感測驅動，延伸軟換相的控制方法，調整功率開關的空白時間，使線圈上的電流產生不連續導通的狀態，偵測其反抗電動勢的零交越點即為電流的換相點。為了解決無感測啟動的問題，本文配合單相馬達非對稱氣隙的特色，使用特殊的啟動機制，不論轉子初始位置在哪裡，皆可使馬達往既定的方向旋轉，並以kick-off的方式加速馬達，直到反抗電動勢大小足以提供無感測演算法正確的運作，便可切換到無感測驅動模式。在無感測驅動下，亦使用閉迴路電流模式的控制方法來提升風扇馬達的運轉效率，而電流命令係利用查表的方式來取代霍爾感測器的訊號。本文使用數位訊號處理器(TMS320LF2407A)驗證所提出控制策略的可行性與性能。實驗結果顯示，在有感測控制下使用效率最佳化的控制方法，其直流鏈電流的平均值至少有12%的改善，其相電流的方均根值至少有10%的改善，其相電流的峰值至少有42%的改善；在無感測控制下，可使風扇馬達穩定啟動並操作在廣泛的速度範圍，而且其運轉效率幾乎與有感測的結果相同。

This thesis develops efficiency optimization control strategies for single-phase brushless dc (BLDC) fan motors with or without Hall sensor. A simple modeling method with feasible parameter identification is proposed to meet characteristics of single-phase BLDC fan motor. The nonlinear rotor flux distribution is modeled by a look-up table. With simulation assistance, the proposed model has been verified with measurement results. This thesis compares the different control strategies include open-loop voltage-mode control of hard-commutation scheme, open-loop voltage-mode control of soft-commutation scheme, and closed-loop current-mode control scheme, and analyzes the current response and overall efficiency. With the linear Hall sensor feedback, the advantages of current-mode control scheme and soft-commutation scheme are adopted to achieve maximum efficiency over the entire speed range. This thesis also develops a low-cost and high efficiency sensorless control for single-phase BLDC fan motor drives. The proposed scheme detects the back-EMF zero-crossing-point (ZCP) to realize current commutation without Hall sensor. An adjustable blanking time control method is used to ensure correct detection of the ZCP. To overcome the sensorless start-up problem, a specific strategy based on characteristic of asymmetric air gap is developed to ensure the motor running in predefined direction. Then, an open-loop control called kick-off speed up the fan motor to middle-speed where sensorless control algorithm based on the back-EMF can work properly. The closed-loop current-mode control scheme is also applied to improve the overall efficiency. However, the current reference is produced by look-up table to estimate the Hall sensor signal. Experimental implementation has been constructed on a single-chip DSP controller (TMS320LF2407A) to verify the performance and feasibility of the proposed control strategies. When using the control scheme with Hall sensor, experimental results show that there are at least a 12 % reduction for average value of dc-link current, a 10 % reduction for RMS value of phase current, and a 42% reduction for peak value of phase current. When using sensorless commutation control, the fan motor can start-up smoothly and operate under wide speed range, moreover, the overall efficiency is almost the same to the results of control scheme with Hall sensor.