A multiobjective-optimal neuro-fuzzy extension to power plant co-ordinated control

This paper presents an overall control scheme for wide-range multiobjective-optimal operation of a fossil-fuel power unit. The scheme provides the means to accommodate operating scenarios characterized by multiple operating requirements, and to attain optimal operation along any arbitrary unit load-demand pattern. The proposed strategy builds upon current coordinated control schemes, which typically account for simultaneous control of power and steam pressure. First, the scope of coordination over the internal processes of the unit is extended by including the control of the drum water level to achieve balanced overall plant operation at all loads. Then, a supervisory reference governor and a neuro-fuzzy feedforward control path are added to complement the already existing multiloop feedback control conguration. The reference governor implements a set-point scheduler based on unit load demand to set-point mappings, which are designed by solving a multiple objective optimization problem. The feedforward control path approximates the nonlinear multivariable inverse static behaviour of the power unit at the optimal operating conditions specied by the set-point mappings through a set of multi-input–single-output fuzzy inference systems, which are designed using a neuro-fuzzy learning paradigm. With this approach, the plant is driven by an arbitrary unit load-demand pattern from which the reference governor species the multiobjective-optimal operating conditions for the plant through set-point trajectories; the feedforward control path provides control signals to achieve wide-range manoeuvrability and the feedback control path compensates for uncertainties and disturbances, along and around the commanded set-point trajectories, respectively. Simulation results demonstrate the feasibility of the proposed control scheme. 130 A multiobjective-optimal neuro-fuzzy extension to power plant coordinated control Nomenclature E uld Unit load demand (MW) E (E d) Electric power (reference) (MW) P (P d) Steam pressure (reference) (kg/cm 2) L (L d) Drum water level deviation (reference) (m) r f Fluid (steam-water) density (kg/cm 3) u 1 (u 1 ff , u 1 fb) Fuel control valve demand (feedforward, feedback) (p.u.) u 2 (u 2 ff , u 2 fb) Steam control valve demand (feedforward, feedback) (p.u.) u 3 (u 3 ff , u 3 fb) Feedwater control valve demand (feedforward, feedback) (p.u.) a s Steam quality q e Evaporation rate (kg/s) E spm Unit load demand to electric power set-point mapping P spm Unit load demand to pressure set-point mapping L spm Unit load demand to level deviation set-point mapping V i Feasibility region of ith decision variable J(·) k-dimensional vector of objective functions J i (·) …