1、附录 2 Study and Design no Automation Control System of the Thermal Power Unit from the System Point of view. Tian Jianyan liu sifeng Pan lizhen （ 1. NanjingUniversity of Aeronautics and Astronautics ,Nanjing 210016 China) （ 2. TaiyuanUniversity of Technology ,Taiyuan 030024 China) Abstract: From the
2、system point of view, the feature of the thermal power unit and the demand on its control system are analyzed and research in details in this paper. The character that the boils and the steam turbine are a whole of relative independence is fully considered. By coordinate control, the purpose of the
3、optimal whole operating effect of the system is realize adopting the key techniques of communication, computer and intelligent information process etc. The adaptation and whole property of the system is emerged by interaction and coordination between subsystems. 1Introduction The system is an organi
4、c whole certain structure and function ,which consists of several element with interrelation , interdependence and interplay .The thermal power unit is a typical system ,composed of generator ,steam turbine ,boiler and many anxiliary equipment .Its main function is to produce the power load accordin
5、g to power network requirement .System engineering is the science used to study and design the complex system .In the meantime, It is also the theory and method used to deal with systems in term of definite aim in order to achieve the optimal whole of the system .From the system point of view, the c
6、oordinate control system of the thermal power unit has been studied and designed in this paper . 2 Study and Design on Automation Control System of the Thermal Power unit from the System Point of View 2.1 Function of Automation Control System of the Power unit At first the thermal power unit as the
7、controlled object is deeply studied before its automation control system is studied and designed .The thermal power unit is a huge group of equipments ,which is composed of generator, ,steam turbine ,boiler and many auxiliary equipments. Its process flow is complex and pipelines intervenient .Especi
8、ally the large-scale power unit is a typical coupling ,nonlinear ,varying complex controlled object with multi-input and multi-output .Thousands of parameters are measured ,operated and controlled .The character of object is changeful because of many different operating modes and switch relation .Wi
9、th enlarging of industry production scale and the raising of peoples living standard ,the required quantity of power energy is increasing and the difference of apex and vale of power load is increasing .So the new and higher require is put forward for automation control system of the power unit . （
10、1.） Load control :Along with the increase of the unit capacity ,early load control mode of “boiler follows steam turbine ”or “steam turbine follows boiler ” has not already satisfied the requirements so we must adopt more suitable load control scheme ,which is the unit coordinate control . （ 2.） Rel
11、iability: The design of system must be reliable, ensuring safe and economic operation of the unit .In addition, The tolerance fault, redundant technology ,self-diagnosis of software and hardware must be adopted to improve the reliability of system . （ 3.） Communication and man-machine interface: Bec
12、ause there are many parameters need to be measured and controlled and its varying speed is quick when the large scale unit is running , communication system must have quick real-time response and high reliability ；man-machine interface must be good at the operator station including operating termina
13、l and large-area display that provides synthetic menus and information about the whole production process for the operators. 2.2 Structure of Automation Control system of the power unit The design of automation control system of thermal power unit mainly includes control, alarm monitor, protect etc
14、. In accordance with the above analysis .So we divide the complex system into several subsystems in order to make the whole system optimal . （ 1.） Data acquisition system(DAS):It is information center of whole system and provides credible rapid objective operating records ,which is the base of safe
15、and economical operating of equipments .Function of ,print of accident list and incident review ,property calculate ,operate guidance etc （ 2） Boiler control system :Boiler control system such as boiler combustion ,steam temperature ,feedwater ,auxiliary control system and the boiler safe supervisor
16、y system and boiler combustion management system. There subsystem coordinate each other and make boiler operate in safe ,efficient and steady state to satisfy the load instruction of power network in various operating modes . （ 3.） Steam turbine control system :Steam turbine control system realizes
17、load control and rotative velocity control of steam turbine by DEH (Digital Electro-Hydraulic ).In addition ,the auxiliary system of steam turbine include the deoxygenation water lever control ,deoxygenation pressure control ,the condenser hot well water level control and the heater water lever cont
18、rol etc （ 4.） Auxiliary system :Besides the main systems mentioned above ,the auxiliary system also has by-pass control system etc The main system and auxiliary system are a organic whole through close connection of information communication network .They are inter-permeable and .Inter-dependent so
19、as to form the main part of the automation control system of the large-scale unit. 2.3 Design of Automation Control System of the Thermal Power Unit From the system point of view, we analyze and study the principle of two basic feedback control method early that “boiler follows steam turbine” and “s
20、team turbine follows boiler” in order to find out the existent problem ad be able to design more reasonable control method. 2.3.1 Boiler follows steam turbine mode This kind of control mode is first to let steam turbine trail the needs of power network load ,then let boiler trail steam turbine .Its
21、advantage is to be able to fully use the heat accumulation of boiler ,make the unit meet the change of power network load comparatively quickly. But because the inertia and delay of boiler are greater ,the regulation of former turbine pressure pt cannot follow the speed of load regulation, thus pt h
22、as greater fluctuation, which is disadvantageous to the steady operation of boiler .The range and speed change of the units output must be restricted . 2.3.2. Steam turbine follows boiler mode This kind of control mode is first to let boiler train the needs of power network load, then let steam turb
23、ine train boiler .It can be better to maintain steam pressure stabilize and beneficial to boiler steady operation .But it do not fully utilize the heat accumulation f boiler to regulate the units output ,it is more slowly that the unit meets the loads demand ,so this control mode is only to be appli
24、ed to the unit undertaking basic load . 2.3.3 Coordinate control mod According to the analysis above, it must use the heat accumulation of boiler fully and reasonably when the unit has better adaptability to power network load in safe operation. That is to let former turbine pressure changes, then t
25、o coordinate the interaction between two loops of power regulation and pressure regulation reasonably, so that units output meets the needs of the power network load promptly, and guarantee the control demand of unit steady operation. The practical method is to lead into properly feedforward control
26、 systems mentioned above and make boiler and steam turbine coordinate each other so that the schemes of various coordinate controls suitable to practical project can be attained, such as: coordinate control system based on“ boiler follows steam turbine” or“ steam turbine follows boiler”。 2.3.3.1. Ba
27、sic function of coordinate control system. Coordinate control system of the thermal power unit should usually have following function:(l) select different load instruction according to the unit operating condition and the requirement of power network for the unit.(2) restrict the change rate of load
28、 instruction.(3). Calculate the biggest possible output of the unit and restrict the biggest and minimum amplitude of load.(4). Have the function of RUNBACK.(5). Select different running mode according to the unit operating condition.(6). Calculate actual unit output.(7). Let automation control syst
29、em have enough steady abundant quantity and better wholeness.(8). Have necessary safe measures such as starting by-pass system and preventing steam turbine from exceeding the speed limit etc, when the unit and power network unite suddenly because of accident. 2.3.3.2 Basic composition of coordinate control system of the unit. Now the coordinate control system of the unit is composed of two parts, which are load instruction process and coordinate control of boiler and steam turbine, shown as fig.1.
