Beam Pumping Unit Modeling And Automatic Control System Design

Beam pumping unit is widely used in oil field for the benefit of simple structure, convenient maintenance, long using life and so on. But it also has some problems such as low efficiency, high energy consumption and low automation degree. Based on these problems, variable frequency technology is used to reconstruct pumping unit for saving energy, the frequency is adjusted dynamically, velocity of up and down stroke is changed according to actual needs to make the oil extracting system run at its best status.By analyzing the work theory of beam-pumping unit, a beam pumping unit model is established. The kinetic characteristic and dynamic characteristic simulation have been made. According to mechanical system dynamics principle, beam sucker rod pumping system is simplified to an equivalent model. The motor axis is regarded as equivalent component part, thus an equivalent differential equation is set up and solved. Combined with variable frequency energy saving idea and teaching characteristic of the major itself, variable frequency speed adjusting automatic control system based on programmable logical controller is designed, and closed-loop control of pumping system is realized. Programmable logical controller received signals from pumping unit transducers, and then disposed them by internal procedure and sent output signals to frequency converter. Frequency converter varied output frequency to adjust the speed of motor dynamically, so that the speed of beam pumping unit can be real time changed along with the need of work situation. PID controller is applied to the experiment platform.Upper computer is used for data acquisition and saving. Man-machine interface is used to operate the system. The whole system that is controlled by network is simple, convenient and easy to handle. On the basis of analyzing mathematical models of pumping system components, closed-loop control system of beam pumping unit is simulated by Simulink software, and PID and fuzzy PID controllers are applied to the system.The experiment platform which was passed actual test and is being used now is designed according to the actual field status. Good effect will be acquired if it is used for either practical teaching or research work. Closed-loop control is introduced to the pumping system; so that the long-term existing problem of open-loop is solved, the automation degree is improved. It will bring great economic and social benefits.