Top Drive Torque Control for Stick-Slip Mitigation
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Solution Overview
Problem
Existing stick-slip mitigation systems in underground drilling are limited by slow speed control loops, which hinder their ability to effectively manage higher frequency torsional vibrations, leading to reduced down-hole tool life and increased wear on drilling components.
Innovation Solution
Implementing a control system that switches to torque control mode, utilizing a fast torque control loop in conjunction with a slow integration speed control loop, allowing for quicker response times and better management of torsional vibrations by directly comparing actual torque measurements to target values and adjusting motor speed accordingly.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If speed control loops are used to modulate RPM for stick-slip mitigation, then torque smoothness is improved, but response time deteriorates due to the slower nature of speed control loops compared to torque control loops
Solution Approach 1:
The control system is segmented into two distinct control loops: an outer speed control loop that modulates RPM to achieve torque smoothness, and an inner torque control loop that provides fast response for stick-slip mitigation. This segmentation allows each loop to specialize in one function, resolving the contradiction between torque smoothness and response time.
Solution Approach 2:
The solution adds a new control dimension by introducing a torque control loop that operates in parallel with the speed control loop. This creates a hierarchical control structure where the torque loop operates at a faster timescale, effectively adding a temporal dimension to the control system that enables simultaneous achievement of both smooth torque and fast response.
2Stability of the object's composition
If speed control loops are used for stick-slip mitigation, then torque control is achieved, but the ability to mitigate higher frequency harmonics deteriorates due to delay in generating RPM and torque commands
Solution Approach 1:
The control system separates torque control functions into two segments: the outer speed control loop handles fundamental torque control and RPM modulation, while the inner torque control loop specifically handles high-frequency harmonic mitigation. This segmentation enables precise mitigation of higher frequency harmonics that would otherwise be lost in the delay of the speed control loop.
Solution Approach 2:
The torque control loop acts as an intermediary between the speed control loop and the motor execution. It receives torque commands from the speed loop, processes them with minimal delay, and directly controls motor current to achieve both the commanded torque and rapid response to high-frequency vibrations, thereby bridging the gap between slow speed control and fast motor response.
3Speed
If torque control mode is used instead of speed control mode, then response time is improved, but integration with speed control deteriorates without a slow integration loop
Solution Approach 1:
The solution merges the torque control loop and speed control loop into a unified hierarchical control system. The outer speed loop generates reference torque commands based on desired RPM profiles, while the inner torque loop executes these commands with minimal delay. This merging allows both control objectives to work together seamlessly, integrating fast torque response with overall speed control.
Solution Approach 2:
The speed control loop performs preliminary action by generating torque reference commands in advance based on the desired RPM profile. These pre-calculated torque references are then fed to the torque control loop, which executes them with minimal delay. This preliminary planning allows the fast torque loop to operate within a structured framework, reducing the complexity of coordinating both control objectives.
Data Source
AI summary
A control system that mitigates stick-slip vibrations at higher harmonics than currently available is disclosed. A controller of a top drive is set to a torque control mode instead of a speed control mode. The controller receives torque measurements and compares to a target torque value. The controller accelerates or decelerates the top drive by a generated current adjustment command. A slow integration speed control loop, at least an order of magnitude slower in response than the torque control loop, receives a RPM set point. The slow integration speed control loop compares the RPM set point to an actual RPM measurement and generates a torque command. The torque command is sent to the torque control loop which results in an acceleration or deceleration of the top drive to maintain a desired torque amount. The speed of the top drive is bounded by a speed limit control loop.