Research On Dynamic Characteristic Analysis And Robust Optimal Control Of District Heating System

With the topology of district heating(DH)networks becoming more complicated,the increasing demands on terminal thermal comforts and the enlarging pressures on energy reduction of DH systems,the innovations and improvements of operation techniques on DH systems are urgent.Hence,the thesis focuses on hydraulic and thermal modeling,dynamic characteristic analysis and operation strategies of DH network.The thesis developed numerical calculation method of the transient hydraulic model of DH network.The dynamic responses of heating substation flow rates to the actions of heat source pumps and heating substation valves were studied based on a DH network case.The numerical method for transient hydraulics of DH network can be the basement of DH system flow response analysis during hydraulic operation.An implicit upwind scheme was proposed for the thermal transient calculation of DH pipeline.The new method is fast and unconditionally stable.The frequency domain closed-loop stability analysis criterion of heating substation was developed,and the oscillation phenomenon of the heating substation was revealed.The frequency domain closed-loop stability criterion of heating substation and the controller tuning principle for robust stabilization were developed.Analysis on the closed-loop stability of heating substation shows that the feedback controller will not ensure robust stability if the controller is only tuned around a certain condition.An effective optimal strategy of hydraulic condition operation based on the general reduced gradient optimization method was developed for optimal operation of DH network with multiple heat sources and meshed topologies.The objective function is the total pump power of DH network,and the heating substation flow rate demands and hydraulic balance equations are the constraints.The optimal heat source pump speeds and heating substation valve openings can be calculated with the optimal operation strategy.Compared with the constant pressure difference strategy,the optimal operation strategy can reduce the pumping power of DH network by 20%.In order to improve the dynamic performance of district heating substation and room heating system,the two-degrees-of-freedomH_?loop-shaping controllers were designed for district heating substation and room heating system,which can ensure good and robust reference tracking and disturbance rejection performances under model uncertainties and different disturbances.