On Advanced Control Strategy And Its Applications To Unit Coordinated Control Systems

Unit plant has some advantages, such as simple system, short steam pipe, few valve and pipe accessory, and short generator bus, which makes less investment, simpler operation, less accident and unit sliding-parameter running and startup or shutdown better. In addition, the unit also facilitates the centralized operation for the boiler, turbine and generator. Therefore, the unit account for high proportion in power plant in china. With the continuous demand of electricity, the progress of science and technology and high requirement of unit economical performance, main characteristics of power industry is focused on the large capacity and high parameters good automation technology for the unit plant. In present, the control strategies of the unit coordinated control system still depend on PID and feed-forward compensation theory. Because of complex control objects, unit plant involves several domains and multivariable in its equipment and principle, and has some features of time-delay and time-varying nonlinear dynamic property. Furthermore, traditional control strategy based on single loop model limits the quality of the control system. So it is significant to explore advanced control strategy to enhance power process.Boiler and turbine are combined into a control object in traditional method, which is adjusted by internal coordination to satisfy the requirement of power network load to the greatest extent. Then, coordinating the internal relationship becomes the major problem of main control system of unit plant. In addition, the main control system is the core of coordinated control system, and is the instruction system of the whole unit plant in automatic regulation. Signal from external requirements for the load of the unit plant is processed and transformed by main control system for better operation states of plant and boiler. The main control system is the key part of the unit generator with instructions which is used to coordinate the boiler and turbine better, is an indispensable core of modern automatic power plant. In this paper, the design and realization of the unit coordinated control system are studied based on the linear multiple-variable control and nonlinear control theory and methods in order to enhance the application of advanced control strategy and improve the adaptability of coordinated control system for the nonlinear process.In this paper, we concern with the nonlinear and multivariable thermal object with advanced control strategy, the main research is as follows:For the nonlinear multivariable problem, fuzzy control method and fuzzy adaptive nonlinear control strategy are applied in the load control of unit plant, which solved decoupling model realization and quality of linear controller due to the nonlinear characteristic in unit plant. The nonlinear fuzzy controller of unit plant with fewer rules is designed in a new way for the engineering. For the high order system, the higher derivative of parameter estimation appeared in the control rate. So the adaptive feedback linearization can not be applied in all feedback linearization systems. In order to solve this problem in unit plant, a new method, fuzzy adaptive control based on back-stepping, is proposed, and it has got a good result in coordinated control of unit plant.Main steam temperature of boiler in the unit coordinated control system is a important monitoring and control parameter, and much higher or lower temperature will both have negative influence in safety and economy. Generally, it is required to maintain the main steam temperature at the constant value, which is a difficult problem in the process control of power plant. The reasons are as follows:firstly, there exists time-delaying in the object of main steam temperature. The larger the capacity is, the worse the time-delaying is. So it can not be adjusted in time with the feedback control method; secondly, the dynamic characteristic of main steam temperature is changed with the variant working conditions. It is that the mathematic model is changed with the variant working conditions, which cause bad adjustment with the fixed controller. Furthermore, the dynamic and nonlinear object of main steam temperature can also increase the difficulty of adjustment. For the large time-delaying, nonlinear and time-varying characteristic in process control, fuzzy adaptive method is applied in main steam temperature based on the analysis of practical situation.The adaptive inverse control method is proposed in the application on the complex, unknown and uncertain coordinated control of unit plant. Two methods, inverse system method and fuzzy adaptive inverse control method, are designed for the typical load of unit plant. Finally the simulative results prove the feasibility of these methods.For the MIMO nonlinear unit coordinated control system, a new method is presented based on static neural network, dynamic neural network with some integrators and inverse system method, and it is simple and easy to be realized. After linearization and decoupling for the objects, a closed-loop controller of subsystem is designed with better static, dynamic and anti-interference ability. Of course, the realization process of the method is deeply expatiated.In the end, summary and future research prospect are given.