Independent model space robust control of the shaft torsional oscillation of turbine-generators

The H_infinity torsional modal observer is adopted to estimate the feedback modal signals in the independent modal space (IMS) control loop of the shaft torsional oscillation of turbine-generators. It is proved that the IMS controller can be designed independently, while the inserted H_infinity torsional modal observer has little influence on the distribution of the poles of the closed loop system. Robust stability condition of the IMS controller designed for the controlled torsional mode is derived based on the H_infinity control theory. Moreover, for practical consideration, it is suggested that the controlling torque should be implemented as the component of the generator electromagnetic torque, while the slow dynamic behavior of the mechanical torque is considered as a kind of disturbance. One H_infinity performance specification is proposed to suppress the disturbance. On the basis of the above study, an IMS robust control of the shaft torsional oscillation is developed and formulated as a multi-objective H_infinity synthesis problem. A case study is given to show that the IMS robust control of the shaft torsional oscillation is feasible and effective.