Field-Oriented Motor Control With Adaptive Open-Loop Transition
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Solution Overview
Problem
Existing field-oriented control (FOC) systems for motors, particularly permanent magnet motors, face instability and performance issues during transitions from open loop to closed loop operation due to sudden changes in current vectors, leading to over-current, torque ripple, and potential motor failure, especially at low rotor speeds.
Innovation Solution
A method that transitions from open loop to closed loop operation by ramping the rotor speed until the angle error between estimated and command rotor positions is within a threshold, then switches to closed loop while maintaining a constant current vector, using a coordinate system based on estimated rotor position.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the system transitions from open loop to closed loop operation by changing coordinate systems, then control accuracy is improved, but current instability and torque ripple occur
Solution Approach 1:
The system performs preliminary actions by determining angle error between estimated and command rotor positions before transitioning from open loop to closed loop operation. The transition is conditioned on the angle error being within a threshold, ensuring the system is ready for coordinate system change. The current vector is held constant during the transition to prevent instability.
Solution Approach 2:
The system changes operational parameters by switching from open loop control to closed loop control, and from command-based coordinate system to estimated-position-based coordinate system. The transition is managed by changing the control mode parameter and coordinate system parameter while maintaining current vector magnitude and phase to ensure stability.
2Measurement precision
If the coordinate system changes from command rotor position to estimated rotor position, then sensorless control accuracy is improved, but over-current and torque ripple occur
Solution Approach 1:
The system validates the angle error between estimated and command rotor positions before initiating the coordinate system change. This preliminary check ensures that the estimated rotor position is sufficiently accurate to support the transition to closed loop operation, preventing harmful effects from inaccurate position estimation.
Solution Approach 2:
The system cushions the transition by holding the current vector constant during the coordinate system change. This prevents sudden current changes that would cause over-current conditions and torque ripple, while still enabling the beneficial coordinate system transition for improved position accuracy.
3Loss of time
If the transition is performed quickly, then response time is improved, but motor damage may occur
Solution Approach 1:
The system performs necessary preparations before the transition by calculating and validating the angle error. This ensures the transition can proceed safely and efficiently when conditions are met, optimizing the response time while maintaining reliability.
Solution Approach 2:
The system protects against motor damage by holding the current vector constant during the transition, cushioning against harmful current spikes. The transition is enabled only when angle error is within threshold, preventing unreliable operation while maintaining efficient response.
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 stabilizes the motor transition, reducing instability, avoiding over-current and torque ripple, and enhancing motor efficiency and reliability, thereby preventing damage and improving startup performance.
Implementation Method 1
Electrical signals through the windings generate a rotating magnetic field that interacts with the magnets of the rotor, causing the rotor to rotate
Data Source
AI summary
In described examples, a device includes a processor and a non-transitory memory storing instructions that, when executed, cause the processor to operate in an open loop mode a motor that includes a rotor and a stator. An angle error of the rotor is determined. In response to the angle error of the rotor being less than a threshold, the processor transitions from operating the motor in the open loop mode to operating the motor in a closed loop mode by changing from using a first coordinate system based on a command rotor position to using a second coordinate system based on an estimated rotor position to determine current vectors used to control the motor; and holding constant a current vector used to control the motor while performing the changing action. After performing the changing and holding actions, the processor operates the motor in the closed loop mode.