A zero-phase-lag torsional filter for large turbine-generators based on the general observer

The large turbine-generator units have more potential of the torsional interaction with the decrease in the torsional mode frequencies of the shaft system and the increase in the bandwidth of the control systems. A zero-phase-lag torsional filter based on the general observer is developed as a generic countermeasure against the torsional interaction with the control systems in this paper. Different from the general torsional filter, the proposed filter can selectively minimize the torsional oscillation component while the rigid rotation speed is all-pass with zero phase lag, and furthermore, provide additional degrees of freedom which can be used to implement synthesis of some performance specifications for robustness requirements. The synthesis procedure of the zero-phase-lag torsional filter is formulated as a mixed sensitivity problem based on the loop shaping approach. A case study based on the IEEE first benchmark model is given to illustrate the design procedure and performance of the zero-phase-lag torsional filter.