Dynamics and frequency and voltage control of downhole oil pumping system

Abstract

The motor load torque of a typical pumping system employed in onshore oil-fields has a fluctuating ‘double-hump’ profile, which requires a motor with a substantially higher rating than the average load torque. In this paper, we have developed a dynamical model of this electro-mechanical system. To reduce the load fluctuation and consequently lower the required motor rating and energy consumption, a real-time voltage and frequency optimization scheme (RTVFOS) is proposed. Both real-time frequency optimization scheme (RTFOS) applying constant voltage and frequency ratio principle as well as real-time voltage regulation scheme (RTVRS) with constant frequency are also simulated. It is shown that the RTFOS is capable of substantively decreasing the motor rating while the RTVRS is capable of delivering a significant energy savings. It is demonstrated that the RTVFOS combines the benefits of both control methods and also lowers the range of variation in voltage, thereby improving the motor’s operating life.