Variable Speed Pump Torque Control for Fluid Density
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Solution Overview
Problem
Conventional multi-phase fluid pumping systems are unable to quickly react to changes in gas volume fraction and fluid density, leading to potential pump instability and failure due to slow differential pressure changes and rapid density variations.
Innovation Solution
A system that monitors a first system parameter, such as differential pressure, and sets a target value for a second system parameter related to pump torque, using controllers to regulate the pump's rotational speed and maintain operation within a permissible region by minimizing the difference between monitored and target values of the second system parameter.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If differential pressure control is used to regulate pump operation, then the pump can be kept within permissible operating region, but the system cannot react quickly to rapid changes in gas volume fraction and fluid density
Solution Approach 1:
The system implements a feedback control mechanism where the motor current (which reflects torque) is continuously monitored and fed back to the control unit. The control unit compares the actual motor current with a reference current and adjusts the motor speed accordingly to maintain the pump within its permissible operating region, enabling rapid response to density changes while ensuring operational stability
Solution Approach 2:
The invention changes the control parameter from differential pressure to motor current (torque). Since motor current responds immediately to changes in fluid density and gas volume fraction, this parameter change enables the system to react quickly to rapid fluid property changes while maintaining reliable pump operation through continuous torque regulation
2Reliability
If conventional differential pressure monitoring is used, then pump operating region can be controlled, but the control system is too slow to prevent pump instability during rapid density variations
Solution Approach 1:
The system takes preliminary action by monitoring motor current, which provides an immediate indication of changing fluid density and load conditions. By detecting torque changes before they lead to unstable operating conditions, the control system can proactively adjust motor speed to prevent pump instability and failure, rather than reacting after differential pressure changes occur
Data Source
AI summary
A method of operating a system (16) for pumping a fluid, which system comprises: a pump (17) for pumping the fluid; and a variable speed motor (20) for driving the pump (17). The method comprises the steps of: identifying a first system parameter (PI); identifying a second system parameter (P2) which is a function of the torque of the pump; setting a target value (P10) for a first system parameter; monitoring the first system parameter (PI); establishing a target value (P20) for the second system parameter based on the difference between the target value and the measured value of the first system parameter; monitoring the second system parameter; and regulating the rotational speed of the pump such that the difference between the monitored value and the target value of the second system parameter is minimized. A system for implementing the method is also disclosed.