A fuzzy control system for motor drive in urea production

A novel fuzzy PI hybrid control system for a variable frequency variable speed drive is introduced, which has been successfully used to control the level in a urea absorbing tower. Its main drive system consists of frequency converter and squirrel cage asynchronous motor to improve the reliability, maintenance, energy saving and production efficiency. The fuzzy PI hybrid control based on a 8031 single chip microcomputer is utilized as a closed loop control strategy. In this strategy, fuzzy control is employed under the condition of large deviation; and PI control is used in the case of small deviation. It has realized the steady closed loop control for large capacity frequency converters and controlled systems which includes strong nonlinearity, large inertia and large time lag. The practical operating has shown that this system has a quicker dynamic response, smaller overshoot, and stronger robustness compared with PI control and has higher steady state accuracy compared with conventional fuzzy control. Moreover, this system has a high reliability and substantial effects in energy saving.