Large Power Plants Feedwater Intelligent Control System

With the development of process control technology the requirements of automatic control level for generating unit are increasing rapidly. Full range feedwater control system is one example. Both units (2X300MW) of one power plant in India, designed and constructed by China, employ feedwater system composed of three 50% capacity motor driven feedwater pumps, one low load feedwater control valve and one main motor-operated-valve. As per the Contract, feedwater control system shall be in automatic mode at full range, and the requirement of drum level control index of feedwater control system is high. In China, feedwater control system of most power plants can not be in automation at full range, especial during low load after synchronization. In addition, the requirement of feedwater control index specified in domestic unit acceptance standard is low than one in Contract. Therefore, normal feedwater full range control system has to be improved in order to meet the requirement in Contract.The paper points out an intelligent full range feedwater control system, based on analyzing dynamic characters of feedwater system and fuzzy logic theory. The suggested control scheme fulfills automatic full range feedwater control by changing the structure and parameter of control system according to different stages of load, making full use of intelligent fuzzy logic function on conditons of remaining process system. During unit startup and load is lower than 15%, drum level is controlled by feedwater control valve, feedwater pump remains at minimum safety speed; when load is between 15% and 25%, feedwater control valve is closing at fixed speed determined by function module, main motor-operated-valve is opened automatically, control mode of drum level is transferred to feedwater pump automatically and bumplessly; when load is between 25% and 50%, control valve is closed fully, and main motor-operated-valve is open fully, drum level is controlled by one pump; when load is more than 50%, first pump is kept in operation, second pump is putting into operation automatically and...