Sensorless Synchronous Permanent Magnet Motor Control
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Solution Overview
Problem
Synchronous permanent magnet motors in downhole environments face challenges in reliable control due to harsh conditions and long conductor lengths, leading to unreliable position sensors and inaccurate estimation methods, which result in instability and potential motor synchronization loss during transients or load changes.
Innovation Solution
A method and system for controlling synchronous permanent magnet motors by supplying each winding with a root mean square supply voltage V=V0+vf_Ratio*f, where V0 is an initial constant voltage and vf_Ratio is a constant ratio of voltage over frequency, allowing for independent control of the power supply without relying on rotor position signals, and determining system parameters like load characteristics and impedance to ensure stable operation and adequate torque generation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If position sensors (Hall effect device, resolver, or encoder) are used to determine rotor position for closed-loop control, then the motor control accuracy is improved, but the reliability deteriorates due to harsh well environment and long cable distances
Solution Approach 1:
The patent extracts the position sensing function from physical sensors and implements it through sensorless algorithms that calculate rotor position from voltage and current measurements. This removes the unreliable position sensors from the harsh well environment while maintaining position determination capability through mathematical estimation based on motor back-EMF and electrical parameters.
Solution Approach 2:
The patent introduces an intermediary calculation method that uses measurable electrical quantities (voltages and currents) as mediators to indirectly determine rotor position. Instead of directly measuring position with sensors, the system uses voltage equations and current measurements as intermediaries to estimate position, bypassing the need for unreliable physical sensors in the well environment.
2Device complexity
If sensorless algorithms are used to deduce rotor position from motor back-EMF, then the device complexity is reduced, but the measurement precision deteriorates at motor start-up and low speeds under load
Solution Approach 1:
The patent applies preliminary action by using direct voltage and current measurements during start-up and low-speed operation to calculate rotor position before the motor reaches steady-state operation. The system performs position estimation using electrical equations at all speed ranges, ensuring accurate torque generation even during transient conditions when traditional sensorless methods fail.
Solution Approach 2:
The patent changes the approach from relying on back-EMF magnitude to using voltage and current parameter relationships. By utilizing the fundamental voltage equations and measuring actual electrical parameters (voltages and currents) rather than relying solely on back-EMF, the system maintains accurate position estimation across all operating conditions including start-up and low speeds under load.
3Productivity
If direct on-line starting methods are used for synchronous motors, then the productivity is improved, but the stability deteriorates because the rotor may lock during acceleration
Solution Approach 1:
The patent applies dynamics by continuously adjusting the stator current magnitude and phase based on real-time rotor position calculations during acceleration. The control system dynamically modifies the electrical parameters to maintain optimal torque production throughout the acceleration process, ensuring smooth and stable rotor speed increase from standstill to operating speed without locking.
Solution Approach 2:
The patent implements feedback by continuously calculating rotor position from voltage and current measurements and using this information to adjust stator current injection timing and magnitude. This closed-loop control based on estimated position ensures that the motor generates adequate torque at each acceleration stage, maintaining stability during the entire start-up process while achieving high productivity.
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 enables stable and efficient motor acceleration from rest to desired operating speeds, even in long conductor lengths, without the need for position sensors, ensuring reliable operation and overcoming transient loads, thus improving the reliability and efficiency of synchronous permanent magnet motor control in downhole applications.
Implementation Method 1
a rotor having permanent magnets, and a stator winding which induces the rotor to turn
Implementation Method 2
The amount of torque to be generated by the interaction of the field with the armature current
Implementation Method 3
sensorless algorithms have been developed which deduce the rotor position from the motor back emf
Data Source
AI summary
A synchronous permanent magnet motor is controlled independently of position sensing means by determining the system parameters including the motor impedance and back-emf and the cable impedance and supplying power according to a predefined voltage:frequency ratio which is determined based on said system parameters to provide a desired rate of acceleration determined by the supply voltage.