在馬達變頻器開關截止時，MOSFET電壓之Vds立即上升，而馬達感性負載為保持其電流量，因此電流無法立即降為零，此時造成開關上的功率損耗並產生熱損使得開關溫度上升，導致開關工作不穩定甚至造成元件燒毀，為達到降低截止時開關之功率損耗，本文提出一控制方法-電流寬度調變 (Current Width Modulation, CWM)。
馬達靠激磁定子繞組使內部轉子與定子相對位置產生改變而旋轉，然而磁通量與定子、轉子之相對位置有關，會造成馬達內部等效電感受磁通量變化而改變，使得電流變化率也有大小不一致的情形。因此我們使用電流寬度調變控制，藉由限制電流來調整ton導通時間，使開關電流峰值不隨角度變動，可降低截止損耗V*I值。另一方面則縮短toff 截止時間，使馬達相電流連續以提供能量。本文將在馬達固定負載且轉速相同的情形下，比較CWM及PWM兩種控制方法操作下之開關電流值及截止時的切換損耗，最後以實驗結果驗證。

As the MOSFET switches off, Vds rises instantaneously. However, induc-tive load of motor keeps the current flowing through it. That is, Ids cannot immediately decay to zero. At this time, power loss is unavoidable. This kind of power loss increases the temperature of MOSFET. Then the device may be destroyed by excessive temperature rise. To reduce the power loss of switching off, this thesis proposes the current width modulation method.
Rotation of the motor relies on the excitation stator winding to make the internal rotor and the stator relative position to change, but the magnetic flux is related to the relative position of stator and rotor. It causes the equiv-alent inductance of the motor to change with the magnetic flux. That makes the current change rate inconsistent. Therefore, the current width modulation control is used to limit the current by adjust the conduction time. So that, the peak of switching current does not change with the angle, which can re-duce v*i value of the switching-off loss. On the other hand, shortening the off-time make the motor phase current continuous to provide energy. This paper compares the current value and the switching loss at turning-off of two control methods between CWM and PWM under the condition of the motor fixed load and the same rotational speed. Finally, Validate the method with experimental results.

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