Shaft Torque Estimation Model for Private Generation System

During disturbances in power system, turbine-generator shaft are subjected to mechanical stress caused by severe torsional torques. Shaft torque is proportional to the shaft twist, which is caused by angle difference between both ends. However, observing the angle difference in an actual generation system is difficult technically. On the other hand, measuring rotational speed of the shaft ends is relatively easy. Then if the shaft torque could be estimated effectively, it would be used in order to control the rotational speed for shaft torque reduction. This paper proposes a shaft torque excitation control for rotating machine by making use of an observer for the shaft torque. Firstly, the relationship between the observation signals and the accuracy of the estimation is discussed. Especially, the range of the error of actual values and measurement values of a turbine parameter are analyzed. Secondly, a shaft torque reduction control system is developed by using excitation control based on the estimate by identity observer.