Optimization And Control Of Organic Rankine Cycle

Improving the comprehensive utilization of energy through waste heat recovery to reduce energy consumption are important measures to alleviate energy and environmental problems.Or-ganic Rankine Cycle(ORC)is a key technology in the field of low temperature waste heat recovery due to its higher thermal efficiency and relatively simple system.In order to improve the ability of ORC waste heat recovery system,this dissertation conducted in-depth research on ORC system parameter optimization and control problems,the main work are summarized as follows:·Aiming at the vehicle ORC system,this paper proposes a thermodynamic steady state model based system parameter optimization method,which effectively improves the overall per-formance of the system.The thermodynamic model of the ORC system is developed to evaluate the effects of sizing the heat exchanger and designing the ORC operating condi-tions on the thermodynamic performance of the ORC system.Considering various major exhaust conditions and the negative impacts of ORC system installation on vehicles,an optimal ORC system design strategy is proposed to maximize the net output power.The optimum geometric parameters of heat exchangers and ORC operating conditions are si-multaneously designed through a mixed integer nonlinear programming problem.The per-formance among the proposed design strategy,the design method without considering neg-ative effects,and the design method only based on one major engine operating point are compared;it can sufficiently reflect the advantage of the proposed approach.·Aiming at the shortcomings of the traditional ORC sequential control design,this paper proposes an structural singular value(SSV)analysis based integrated optimization method of ORC operation condition and control.This method ensures the safe operation of ORC while improving the net output power of the cycle.Traditionally,the closed-loop dynamics of the ORC are not considered in the design of operating conditions,it is easy to violate the constraints of the ORC system during the operation.In order to overcome this shortcoming,the closed-loop dynamic characteristics are integrated into the design of operating condi-tions to make sure the dynamic feasibility.The integrated optimization method maximizes the waste heat recovery and guarantees the safe operation in the presence of disturbances based on SSV analysis.The optimal operating conditions and the controller parameters are obtained simultaneously through a nonlinear constrained optimization problem.The simu-lation results reflect the advantages of the proposed integrated approach.·Aiming at the waste heat condition of large-scale fluctuations,this paper proposes an eco-nomic model predictive control method,which effectively improves the net power output of the ORC system.To maximize the heat recovery and to handle the multivariate con-straints during the ORC transient operation,the economic nonlinear model predictive con-troller(EMPC)with the net power output as an objective is designed based on a reduced ORC dynamic model as predictive model.To fast obtain a solution of EMPC in practi-cal applications,the computation of the gradient of the EMPC objective is simplified and the quasi-sequential method is employed for the online dynamic optimization of EMPC.In addition,the initial values of the EMPC optimization problem are also designed.Unlike the conventional MPC scheme,the results in a case study show that the proposed control strategy can quickly improve the net power output of the ORC system during the operation while still satisfying the load tracking requirements.