本論文旨在研究感應馬達在直接轉矩控制上，馬達在低轉速之電磁轉矩不足與磁通估測誤差大，以及直接轉矩控制法造成馬達運轉時產生轉矩連波等問題，提出濾波器回授、磁通補償與固定磁通變量直接轉矩控制（fixed flux variation DTC）法以降低磁通估測誤差，並使其在低速時能提升輸出電磁轉矩，降低轉矩漣波的策略，減少電流諧波量與功率消耗使馬達運轉更平順，有效降低速度誤差並提高驅動器效能。 首先，針對直接轉矩控制，提出對傳統直接轉矩之磁通估測器的改善方法與改善馬達在低轉速之電磁轉矩不足。主要是因馬達於低轉速時，轉子磁通變化緩慢，若定子磁通仍操作於定磁通情況下，將使定子磁通無法達到有效控制，進而使馬達輸出之電磁轉矩降低、速度誤差大，本文提出提升定子磁通量之補償策略，使其在低速時能有效輸出電磁轉矩，降低速度誤差。其次，對於直接轉矩控制於馬達運轉時，傳統直接轉矩控制法的輸出方式係經由電壓向量表的選擇，輸出適當的電壓向量，此種切換方式無法使功率晶體切換出非常滑順的弦波電壓使得電壓向量間的切換過程中導致轉矩漣波產生，造成高噪音與振動較難於應用於高精密控制，提出固定磁通變量直接轉矩控制FFVDTC設計法則，利用space vector plus width modulation (SVPWM)合成所需電壓向量，控制轉矩輸出大小與磁通增量在一定範圍內以降低轉矩瞬間變量，有效降低馬達運轉時所產生的轉矩漣波。 論文中所提出的方法，經由MATLAB模擬軟體重新建置馬達與控制系統模型，利用模擬驗證其可行後，再以固定點式DSP-based硬體實際測試結果，來證明其性能與效果，藉以佐證出所提出之直接轉矩控制感應馬達驅動系統於工業應用價值。 The purpose of this dissertation is to investigate a novel direct torque control for induct motor. There are drawbacks of direct torque control method for induct motor. These problems include the insufficiency of electromagnetic torque and the large estimated error of magnetic flux while motor operated in low speed, and generating torque ripples. This dissertation provided filter feedback, magnetic flux compensation and fixed flux variation direct torque control method to reduce the estimated error of magnetic flux; furthermore, it provided a strategy of effectively producing the output electromagnetic torque while the motor operated in low speed. Motor could be operated more smoothly by reducing current harmonic waves and power consumption. It could effectively decrease speed error and improve the efficiency of driver. First, a method is provided to modify the magnetic flux estimator of the traditional direct torque control and improve the insufficiency of electromagnetic torque while motor operated in low speed. It is because that the rotor flux changes slowly while motor operated in low speed. If the stator flux is still operated in the fixed flux, the stator flux will not be able to control effectively which may decrease the output electromagnetic torque and increase the speed error. This paper provides a method to raise the stator flux which makes it effectively produce electromagnetic torque in the low speed and reduces the speed error. Second, applying the traditional direct torque control for the motor operation is to select a vector from the list of voltage vector table. This traditional method is not able to geverate a smooth sine wave voltage. Thus it produces torque ripples during the process of switching over between voltage vectors. Torque ripples cause high noise and oscillation. Then it is difficult to apply in the high-accuracy control. This dissertation provides fixed flux variation DTC method which uses the space vector plus width modulation (SVPWM) to compose of the voltage vectors. It effectively reduces the torque ripples during the motor operation. Finally MATLAB simulation software is used to show the possibility of control system. Then it is demonstrated through the fix-point DSP-based hardware. Both simulation and experimental results verify the feasibility of the new-type direct torque control for induct motor drive system.
