The Application And Research Of Frequency Conversion Technology In The Heating System

Heating during winter in north China is a big problem of livelihood, and it is an important part of energy conservation and emission reduction. It is, therefore, an arduous and complicated task to regulate the heat source and heating network effectively not only ensuring livelihood but also saving energy.First, the control system of heat source (mainly about the implementation of frequency conversion of fans and pumps) is optimal designed and retrofitted. On the base of traditional analog control system and distributed control system (DCS), Profibus field bus communication mode is introduced, by which different brands frequency converters with the same communication protocol can communicate with one another.With the equipment layer directly transmitting digital signals, reliability is higher, and the cost of laying, installation and maintenance is lower, and the amount of information is more abundant.After the hardware configuration and parameter setting, field bus can improve the openness, expansibility and human machine interaction of boiler control systems.With duplex communication between computer and intelligent frequency conversion equipment, both abundant instant data and historical data can be read from the field frequency conversion equipment. The information of running condition can be displayed friendlily in the configuration interface and can be managed uniformly and centrally, which provides a solid foundation for optimal control and fault analysis and diagnosis.Second, as for the problem that the pressure of near-end user is too high in heat transmission, excessive pressure is usually cut by using throttle devices such as valves.This technique tends to cause excessive proximal flow, which will result in hot near heat source and cold far from it. To make the temperature of the worst adverse point compliant, wrong decision of using larger pump is often made, which forms a high energy consuming operating pattern of large flow and small temperature difference.Many scholars at home and abroad retrofitted and applied frequency conversion system in substations specifically replaced previous transmission and distribution system, on the basis of research on heat medium transmission theory. Not only is the operational flexibility of the system effectively improved and is hydraulic balance achieved, but the energy consumed in heat transmission and distribution is effectively reduced.Last, as for two or more variable frequency pumps often running in parallel in water distribution, least square method and pump similarity principle are applied for pump characteristic modeling.Characteristic curves of single pump and pumps running in parallel with different speed regulation are drawn. Analytical technique is applied for power analysis when pumps are running in parallel with different speed regulation modes.According to this, a control strategy for variable frequency pumps running in parallel is proposed, and it is verified by experiment.The constructing system in this thesis is of significance in guiding the retrofitting of heating system.