以CPLD為基礎之無刷直流馬達無感測控制之設計與實現

Abstract

本論文之主要目的在於發展一個應用於DVD無刷直流主軸馬達的數位式無感測控制晶片。由於霍爾元件在安裝及使用上的種種限制，本文規劃了一個在沒有霍爾元件回授訊號狀況下的無刷直流馬達轉速控制機制，以偵測未激發相反抗電動勢零交越點的方式，來估算馬達的換相時刻，且藉由分析無刷直流馬達的換相特性，提出一個修正式的反抗電動勢量測法來改善換相點估測的正確性。此外，提出一個新型數位式與頻率無關的相位移器(digital frequency-independent phase shifter, DFIPS)來產生正確的換相訊號。且由於正確的換相控制是無刷直流馬達無感測控制機制關鍵的一環，本文以此相位移器為基礎，實現一個可程式化的相位移補償機制，來補償由於低通濾波器、量測雜訊以及非理想的反抗電動勢波形等原因造成的相位落後，並進一步分析相位移器對於錯誤的零交越點之強健性。另一方面，由於馬達在非常低轉速或靜止的狀況下，無法量測到反抗電動勢，所以必須藉由一個定電流的啟動機制(constant-current start-up control)，使馬達加速至可控的最低轉速，再進入無感測的速度控制。為了改善速度控制響應的效能以達到更大的速控範圍，以反抗電動勢波形為基礎，分析並討論一個修正式的速度估測機制。而設計的流程是先以PSIM模擬軟體，模擬機制的正確性及可行性，再以複雜型可程式化邏輯晶片(Complex Programmable Logic Device, CPLD)作一簡單的驗證，由模擬及實驗可知，以一個高轉速的DVD無刷直流主軸馬達為受控體的情形下，無感測速度控制的速控範圍可以由1000rpm到8000rpm。

This paper presents the design and analysis of a low-cost sensorless speed control scheme for a brushless DC motor (BLDCM). By analyzing the commutation characteristics of the BLDCMs, a special back-EMF measurement method is presented to improve the signal detection performance. Besides, a novel digital frequency-independent phase shifter (DFIPS) is proposed to generate the accurate commutation signals. Since the commutation control is very critical for the BLDCM control, a programmable phase compensation circuit is realized based on the DFIPS to compensate the commutation phase error due to low-pass filtering, measurement noises, and nonideal trapezoidal-shapes of the back-EMFs. The robustness of the DFIPS with respect to the wrong zero-crossing detection is also analyzed. Since the back-EMF measurement can not be achieved at low-speed operation or standstill, a constant-current start-up control scheme is presented to accelerate the motor to a minimum controllable speed, and then the sensorless speed control can be achieved. In order to improve the speed tracking performance with extended speed range, a speed estimation scheme based on the back-EMF shapes is presented. The proposed sensorless control scheme is verified with the PSIM simulation tool, and is realized with a complex programmable logic device (CPLD). Simulation and experimental results show that the sensorless speed control can be achieved for a high-speed DVD spindle motor with the speed range from 1000 rpm to 8000 rpm.