應用類比霍爾感測器及電流重建改善電動輪椅安全與舒適度之研究

Abstract

研究目的在改善手輪馬達電動輪椅的舒適度以及安全性，首先本文選擇利用線性霍爾感測器進行轉子位置的估測，相較於以往的數位霍爾感測器，線性霍爾感測器的解析度較高，且能夠得到轉子位置的初始值，而要能正確的估測轉子位置，首先必須先經過一段訊號的處理，接下來才能夠進行轉子位置的估測，獲得正確的轉子位置後，即可將其應用至磁場導向控制進而驅動手輪馬達，相較於六步方波，磁場導向控制不但驅動效率更高，且能夠控制在更為低速的範圍，對於使用者啟動的舒適度能夠有更佳的幫助，且由於其是針對每個角度形成垂直的磁場進行驅動，因此馬達在轉動所產生的震動較低，也能夠提供使用者更好的使用體驗。 而實現磁場導向控制需要利用空間向量脈寬調變，並且為了完成閉迴路則必須將電流做取樣，並且輸入控制器，目前最常使用的電流取樣方式為在三相下橋與直流負端間放置取樣電阻，進而取樣三相電流，也因此下橋的導通時間成了很重要的角色，因為若是無法提供足夠的下橋導通時間可能會造成電流錯誤取樣，而這些無法正確取樣電流的區域在空間向量脈寬調變中稱為電流死區，本文針對不同的電流死區利用不同的策略來完成電流重建，避免系統過度補償而產生暴衝的現象，增加了電動輪椅的安全性。 完成以上控制策略後，首先會將速度與電流與前一代的控制系統比較，接下來會比較電流重建前後的電流差異。

The purpose of the thesis is to improve safety and comfort of powered wheelchair driven by rim motors. This research use analog hall effect sensor to estimate rotor position instead of digital hall effect sensor. Because analog hall effect sensor has higher resolution and it can provide initial motor position inform. To obtain more accurate rotor position , hall effect voltage signal processing is necessary before estimating rotor position,. After rotor position estimation, we can use the result to implement field oriented control(FOC). Compared to six step square wave control, field oriented control not only has higher motor efficiency but can let motor operate in lower rotating speed. These advantages can let users of electric wheelchair feel more comfortable when they start to operate the rim motors. In addition, FOC can provide users with a better, because it use different vertical magnetic field for each angle. To achieve the field oriented control, it is necessary to use the space vector pulse width modulation, and in order to complete the closed loop, the current must be sampled. The most commonly used current sampling method is to place a shunt resistor between the lower bridge switch and dc-link negative line , and then sample the three-phase current. Therefore, the lower bridge switch conduction time becomes an important role, because if the lower bridge conduction time cannot be provided, the current may be sampled incorrectly. These areas where the current cannot be correctly sampled are called current dead zone. In this paper, different strategies are used to complete the current reconstruction for different current dead zones, avoiding over-compensation and sudden unintended acceleration, and increasing the safety of electric wheelchairs. After completing the above control strategy, the speed and current will be compared with the previous control system, and then the current difference before and after current reconstruction will be compared.