Induction Motor Torque Control in Pumping Systems
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Solution Overview
Problem
Existing methods for controlling the speed of induction motors in pumping systems, such as those used in the oil and gas industry, are inefficient and prone to inaccuracies, leading to undesirable operational conditions like lower or higher than expected pump speeds, which can result in damage and reduced pump life due to inadequate control over the motor's rotational speed.
Innovation Solution
A system and method that control the rotational speed of the motor by using a first control feedback loop to manage magnetic flux and a second control feedback loop to manage motor speed, both based on electrical input measurements, allowing for precise control of the motor's operation by adjusting the generator's field excitation and engine throttle position.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a variable speed drive (VFD) is used to provide variable speed operation of the pump, then the pumping system capability is greatly expanded, but voltage harmonics are generated on the motor leads that can damage the motor and current harmonics are generated at the input of the VFD that can cause problems for the generator
Solution Approach 1:
The patent extracts the speed control function from the electrical power conversion system by using a mechanically coupled clutch assembly between the engine and generator. This removes the need for a VFD, eliminating the harmful voltage and current harmonics while preserving variable speed capability through mechanical means.
Solution Approach 2:
The patent introduces a clutch assembly as an intermediary mechanical device between the engine and generator. This mediator enables smooth engagement and disengagement of the generator from the engine, providing variable speed operation without electrical power conversion and its associated harmonic problems.
2Adaptability or versatility
If an electronic variable speed drive is interposed between the generator and the induction motor, then variable voltages and frequencies can be provided to the motor, but the complexity in VFD design and the need for an expensive output transformer increase when higher voltages are used
Solution Approach 1:
The patent removes the complex VFD electronics and output transformer by using direct mechanical coupling through a clutch assembly. The variable speed operation is achieved mechanically rather than through complex electrical power conversion equipment.
Solution Approach 2:
The patent replaces the electrical/electronic speed control system (VFD with transformer) with a mechanical speed control system using a clutch assembly. This substitution eliminates the need for expensive and complex electrical equipment while achieving the same functional result.
3Ease of operation
If the output speed of the induction motor is allowed to vary based on pump loading without active control, then the system is simpler to operate, but the pump may operate at lower than expected speed resulting in lower than optimal production or at higher than desired speed causing pump dry conditions
Solution Approach 1:
The patent implements a feedback control system using a speed sensor to monitor the actual pump speed and a controller to adjust the clutch engagement accordingly. This feedback mechanism maintains accurate speed control while preventing pump dry conditions, balancing simplicity with reliability.
Solution Approach 2:
The controller proactively adjusts the clutch engagement before pump dry conditions can occur by monitoring speed and loading conditions. This preliminary action prevents harmful conditions while maintaining simple operation through automated control.
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
This approach provides precise and accurate control of the pump's operation, reducing the risk of damage and extending pump life by ensuring consistent speed and torque, while also reducing peak starting currents and the complexity of system components.
Implementation Method 1
an engine (e.g., a diesel, gasoline, natural gas, or propane engine) is sometimes used to power a three phase generator. The generator, in turn, supplies power to a three phase induction motor
Implementation Method 2
a three phase induction motor used to drive a mechanical pumping apparatus
Data Source
Figure 1
Figure 2
Figure 3A~3D
AI summary
A system and method are provided for controlling the speed of a motor driving a load that is electrically connected to a generator driven by an engine, through use of a first control feedback loop configured to control the rotor flux of the motor by controlling the field excitation of the generator, and a second control feedback loop configured to control the speed of the motor by controlling the throttle position of the engine.