| 摘要 |
PROBLEM TO BE SOLVED: To avoid the tripping of an electric motor due to the increase in internal temperature in rolling and to obtain an improved plate thickness accuracy. SOLUTION: The internal temperature of an electric motor 3 is estimated, based on an electric motor main circuit current IM to an electric motor 3 for use under pressure, and its temperature change rate α is obtained from the previous value and the current value of the estimated internal temperature when an estimated internal temperature T(t) is an alarming temperature TALM or higher. Then, when the internal temperature tends to increase, an allowable temperature β until the internal temperature reaches the maximum allowable temperature TMAX from the internal temperature T(t) and the temperature change range α and a current-limiting value iLIM is set to a small value as the allowable time β becomes smaller. Then, a current command value i0 based on a speed deviation ΔV of the electric motor 3 is limited by the above current-limiting value iLIM and is supplied to the electric motor 3. Therefore, the supply current to the electric motor 3 is limited and its generation torque is limited, thus suppressing the internal temperature increase and avoiding a situation where the maximum allowable temperature TMAX is reached and avoiding the tripping of the electric motor 3 during rolling. |
