Robust wide-range control of steam-electric power plants

To facilitate daily cycling of large electric generating units that were originally designed for baseload operation, the control system has to be redesigned for plant maneuverability over the operating range. A methodology for synthesizing an integrated feedforward–feedback control (FF/FBC) strategy is proposed for wide-range robust control of commercial-scale steam-electric power plants. In the proposed methodology, the feedforward control (FFC) policy is generated via nonlinear programming for simultaneous optimization of all control inputs under specified constraints. This family of optimized trajectories, which represent the best achievable performance of the plant under specified conditions, serve as tracking signals for the FF/FBC system. The feedback control (FBC) law is synthesized following the H1-based structured singular value ( ) approach to achieve the specified stability and performance robustness. The major features of the integrated FF/FBC system are 1) optimized performance over a wide operating range resulting from the feedforward element and 2) guaranteed stability and performance robustness resulting from the feedback element. To exemplify this control methodology, a family of FFC policies has been synthesized based on a nonlinear state-space model of a 525 MWe fossil-fueled power plant. The synthesis of an FFC policy is identified as an optimization problem where the performance is characterized by rapid maneuvering of electric power to meet the specified load demand while simultaneously maintaining the throttle steam temperature and pressure, and the hot reheat steam temperature within allowable ranges of variation. The results of simulation experiments show that the FF/FBC system satisfies the specified performance requirements of power ramp up and down in the range of 40%–100% load under nominal operating conditions. The results also suggest that this robust control law is capable of rejecting the anticipated disturbances such that the plant closely follows the optimal trajectory determined by the FFC policy. Although this research focuses on control and operation of fossil power plants, the proposed FF/FBC synthesis methodology is also applicable to other complex processes such as planned shutdown of nuclear power plants, take-off and landing of aircraft, and start-up and transient operations of rocket engines.