Shaft torque observer and excitation control for turbine-generator torsional oscillation

In recent years, gas turbines have been attracting a lot of attention in the field of dispersed generations and co-generation systems. The gas turbine generation system always has the problem of the shaft torsional oscillation, and their counter measures that can apply especially for the in-house generating plants at 10MW scale are required. For technical and financial reasons, the number of sensors has to be reduced to an acceptable minimum, and generally it is not possible to measure the torsional oscillations at all critical shaft locations. Thus the torsional oscillations on the crucial components should be estimated by using the measured rotating speed at turbine shaft end. This paper presents the shaft torque observer and coordinated controllers for the in-house generating plants. In this study the turbine model with 7-mass has been used, and the rate of the in-house generating shaft is 5MVA. Linear quadratic regulat or theory (LQR) is used to design the observer gain, which provides acceptable estimated values. The estimation accuracy of this observer is within 10%, and the influence by the measurement error of the shaft parameter is also a little.