ESP Pump Start Control Using Sensorless Motor Speed Estimation
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Solution Overview
Problem
In Electric Submersible Pumps (ESPs) used in the oil and gas industry, it is challenging to determine if the pump is rotating before starting, especially in hard-to-reach locations, as additional sensors are not desirable and predefined delays are not reliable due to changing conditions.
Innovation Solution
Estimating the rotational velocity of an induction motor by supplying a three-phase AC voltage at multiple angular velocities, monitoring the output current, and determining the angular velocity at which specific characteristics in the current are detected, allowing the pump system to operate based on this estimate without additional sensors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a rotary encoder or additional sensor is used to measure pump rotational velocity, then measurement precision is improved, but device complexity and maintenance burden increase
Solution Approach 1:
The AC drive uses its own existing current sensors to monitor motor current characteristics during voltage sweeping. The system self-diagnoses rotational velocity by analyzing current amplitude and power factor without requiring external sensors, making the system self-sufficient and eliminating additional measurement devices
Solution Approach 2:
The AC drive's current monitoring capability, originally designed for basic motor control, is extended to perform rotational velocity measurement. The same current sensors used for control now serve dual purposes: controlling motor operation and detecting rotational state through characteristic analysis during voltage sweeping
2Ease of operation
If a predefined delay is used between pump stop and next start command, then ease of operation is improved, but reliability deteriorates because conditions can change during waiting time
Solution Approach 1:
The system continuously monitors motor current characteristics and uses this feedback to determine real-time rotational velocity. Before each start command, the system checks current measurements to confirm the pump has stopped rotating, ensuring reliable start conditions without relying on fixed time delays
Solution Approach 2:
The system performs a voltage sweep and current characteristic analysis before the pump start command to preliminarily assess the rotational state. This preliminary measurement ensures the pump is stationary before starting, preventing harmful starts while maintaining operational simplicity
3Productivity
If the pump is started while rotating fast, then productivity is improved by reducing waiting time, but reliability deteriorates due to mechanical stress
Solution Approach 1:
The system dynamically adjusts the waiting time before pump start based on real-time rotational velocity measurements. Instead of a fixed delay, the system continuously monitors current characteristics and determines the exact moment when rotational velocity drops below the threshold, enabling optimal start timing that balances productivity and mechanical protection
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Accurately determining if the pump is rotating too fast or not, enhancing pump system reliability and reducing costs by eliminating the need for additional sensors and providing a more responsive operation.
Implementation Method 1
a three-phase induction motor operably coupled to the rotary pump, and an AC drive operably coupled to the induction motor
Data Source
Figure 1
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AI summary
A method and apparatus for operating a pump system comprising a rotary pump (110), a three-phase induction motor (120) operably coupled to the rotary pump, and an AC drive (20) operably coupled to the induction motor, the apparatus being configured to supply the induction motor (120) with a three-phase AC voltage at multiple different angular velocities, monitor an output current of the AC drive (20) generated in response to the supplied voltage at the multiple different angular velocities, determine an angular velocity of the supplied voltage at which at least one predetermined characteristic in the monitored output current is detected and determine a rotational velocity corresponding to the determined angular velocity as an estimate of the rotational velocity of the motor, wherein the pump system is operated on the basis of the determined estimate of the rotational velocity of the motor.