Research of the control system for liquids level maintenance in tanks

Abstract

The problems of controlling the operating modes of pumping units with a frequency-controlled drive based on an asynchronous short-circuited motor are considered. The specific features of the requirements for the control process quality indicators of liquid level stabilization control system for the reservoirs are discussed. Mathematical models of functionally necessary parts of the system are obtained in the form of transfer functions: a frequency-controlled drive with scalar control, a generalized control object, and a feedback sensor. The linearized model of the controlled object taking into consideration a nonlinear dependence of the the torque at the motor shaft on rotational speed is obtained in the form of a transfer function of the aperiodic unit. A block diagram of a closed loop liquid level control system has been developed. It is shown that the use of standard settings for the system under consideration, focused on maximum performance achievement, can leads to unacceptable values of control action speed variations and hence to generation of hydraulic shocks that decreases a wear of kinematic parts of the unit. A method for the synthesis of the controller is proposed, which takes into account the limitations on the quality indicators of the transient process of a speed variation of the pump unit when control system counteracts main disturbances. The synthesis of controller is carried out for an example of a specific installation and the results of modeling transients of a control system and perturbing effects are discussed.