Magnetic levitation for down-hole submersible pumps

Abstract

The feasibility of a magnetic levitation pump for oil well down-hole use is investigated. The design, development, and testing of a closed-loop magnetic levitation pump is presented. This includes the design of the maglev motor, system instrumentation, and mechanical components. The motor angular velocity and motor gap position are controlled with the use of a digital controller. The digital controller utilizes commutation laws for commanding current to the motor based on desired torque and levitation force. The design, simulation, and experimental testing of a proportional controller and a lead compensator for the control of motor velocity and motor gap, respectively, is also discussed. The experimental effort associated with the development of the maglev pump is described in detail. Major topics are the development of models for the system, implementation of control algorithms, and analysis of system response data. Testing verified that motor gap (levitation) and angular velocity are controlled effectively under various pumping conditions. These results prove the feasibility of a closed-loop maglev pump. The pump reached maximum speeds of 1432 RPM during testing, as limited by the motor drive amplifiers. Analysis shows that the pump is capable of reaching 3600 RPM and providing flow and pressure levels equal to conventional submersible pumps, if the current to the motor is increased by a factor of approximately 2.5. Such a current increase is possible without exceeding the thermal limits of the motor. Results show that designing and building magnetic levitation motors for down-hole applications, under the size constraints of current submersible pumps, is feasible. Furthermore, maintaining the levitation gap under pumping conditions and sudden pressure increases is possible through closed-loop control of the motor currents. This work serves as a first step to developing magnetic levitation techniques for down-hole submersible pumps. Suggestions for improvement of the maglev pump are given, and recommendations for future research are presented.