Modeling And Control Of CO₂ Transcritical Power Cycle Based Waste Heat Power Generation Systems

With the increasing demand of the energy consumption,the traditional fossil energy is facing depletion crisis.Increasing the efficiency of energy and developing renewable energy source are two important ways to solve this energy problem coming up today.As a new type of thermodynamic cycle,CO₂ transcritical power cycle can reduce the amount of carbon dioxide,which is widely distributed in the nature.Besides,compared with the conventional steam power cycle,CO₂ transcritical power cycle can make better use of low grade waste heat,improve the utilization efficiency of energy,depress the cost of industrial operation and reduce the contaminant emission.Thus,CO₂ transcritical power cycle is a very promising technology.The operating principle and thermal process of the CO₂ transcritical power cycle are analyzed and two kinds of operation mode,tracking the power load and tracking the waste heat,are shown at first in this paper.Then,the mechanism models of the main components of a CO₂ transcritical power cycle system are established,including evaporator,expander,condenser,and pump.The whole dynamic model can be built by connecting these four subcomponents.The established physical model is with nonlinear characteristics and in state space form.In order to deeply utilize the waste heat resource,a constrained predictive control strategy is presented for CO₂ transcritical power cycle systems.The plant is linearized in vicinity of an operating point before designing the controller.The simulation results show the proposed control method can achieve satisfactory performance in terms of set-point tracking and disturbance rejection.Because CO₂ transcritical power cycle systems are multivariable systems with strong couplings,a multi-loop H? robust control is proposed based on dynamic partial least squares model.It can avoid the complication of decoupling and multivariable control by transforming multi-loop control into several single loop control.This control strategy is applied to the CO₂ transcritical power cycle system.Simulation results show that the proposed control strategy has better set-point tracking ability and disturbance rejection ability than PLS-PID control method.Moreover,the proposed control scheme shows better robustness w model mismatch.