Study On Control Strategy Of Distributed Variable-frequency System

In traditional heating network, the throttle valve may cause a large quantity of power consumption during transmission and distribution. In order to overcome the disadvantage, a new system, the distributed variable-frequency system, has been put forward, which is based on variable frequency pump instead of branch regulating valve. And a such system with pressure balance pipeline is studied in detail in this dissertation.Based on the model of heating system, the types and characteristics of the distributed variable-frequency system are analyzed, with the commonness as well as characteristics of each kind of models obtained. The topological structure of heating network is analyzed by graph theory, and the matrix equation of the distributed variable-frequency system is derived. As a case study, a practical distributed variable-frequency system is analyzed, covering the situation of users, the hydraulic characteristics and the operation of the heating network, etc.Started from the actual problem of the practical system and through dynamic simulation of different processes of regulation, the distributed variable-frequency system shows many advantages over the traditional heating system, from flow characteristics to thermodynamic ones. The existence of pressure balance pipeline makes the heat source and the users(the heat exchange station) possible to be regulated independently, which makes the flow characteristics and thermodynamic characteristics to be of inconsistent between the heat source and users. The characteristics and advantages of the distributed variable-frequency system under accident conditions are summarized through simulation of the state while the heat source pumps stop work.Finally, based on the research on the characteristics of the distributed variable-frequency system, an operational regulation strategy fitted for this system is presented. The feasibility of the strategy is verified by simulation and the energy-saving space is figured out.The research shows that, compared with the traditional heating system, the distributed variable-frequency system with pressure balance pipeline has many advantages, such as lower running energy consumption, easier flow regulation, higher regulating accuracy and better security on system running. However, the existence of pressure balance pipeline makes the thermodynamic characteristics of the system much more complex, which needs a reasonable regulation scheme to direct the heat source running.The reasonable application of distributed variable-frequency system can make the best economic benefit during heat transmission and distribution, which would be of great help to Chinese energy-saving for district heating systems.