Research On Quality Regulation Of Substations In District Heating Based On Model Predictive Control

Overall quality regulation is usually adopted in the operation regulation of existing water heating system.Local operation regulation in substations traces water temperature rather than tracing room temperature directly and the set-point of water temperature is usually set by experience.This kind of regulation in which heat source plays the dominant role limits the regulating capability of substations.With a water-heat-losing and room-temperature-rising link between water temperature and room temperature,water temperature set by experience cannot guarantee room temperature in the presence of varying weather conditions and different levels of heat storage in buildings,that sometimes causes room temperature much higher or lower than the standard.As for this problem,taking weather into account a thermal dynamic model describing the link between water temperature and room temperature of a certain substation heating area is built.Model Predictive Control technique is applied with the thermal dynamic model as prediction model.Supply water temperature of substation is calculated according to room temperature reference trajectory for time-sharing heating.Substation performs operation regulation according to this temperature.The main work of this thesis is as follows.First,in the section of modeling,the features of thermal dynamics and the rationality of describing thermal dynamics with a discrete linear time-invariant state space model are analyzed.Inputs,outputs and sampling period are chosen according to common sense and literatures.Several thermal dynamic models are obtained via subspace identification technique which is a kind of black box identification technique.The validation of models is checked.Models with reasonable responses are chosen as prediction model for model predictive control.Second,a model predictive controller is designed and its parameters are tuned.Considering room temperature being vulnerable to disturbances,an observer applying secondary return water temperature as the single measured signal is proposed.With such an observer,anti-disturbance performances are improved at the cost of slight precision losses.Close loop simulations are performed separately in three intervals.Simulation results of room temperature are compared with historical measured room temperature data.More comparisons are performed under different constraints,turning on previewing feature of measured disturbance signals and in the presence of model mismatch.Third,from the perspective of engineering application,how to get forecasts of inputs is discussed.A two level hierarchy control structure is designed and two kind of different configurations of the upper level are analyzed.Problems in practical operation such as waste of electricity and the unfavorable influences on primary circulation are discussed and strategies are proposed respective to deal with them.Conclusion is drawn from the simulation results.Operation regulation of substation according to supply water temperature of secondary circulation calculated by MPC can make room temperature to trace reference trajectory much better.Room temperature runs steadier.Energy efficiency is improved.Temperature overshoots or not up to standard are obviously improved.Room temperature is still improved even when constrains are changed and even when model mismatch is present.