Field-Oriented Motor Control With Adaptive Open-Loop Start
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Solution Overview
Problem
Existing field-oriented control (FOC) systems for motors, particularly at low rotor speeds, suffer from instability and performance issues due to sudden changes in current vectors during transitions from open loop to closed loop operation, leading to over-current, torque ripple, and potential motor failure.
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 the control coordinate system while maintaining a constant current vector, using estimated rotor position and speed feedback.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the control system transitions from open loop to closed loop operation by changing coordinate systems, then the motor control accuracy is improved, but current vector sudden changes cause instability and over-current
Solution Approach 1:
The system performs preliminary action by determining the angle error between command and estimated rotor positions before transitioning from open loop to closed loop operation. The transition is executed only when the angle error is within a predetermined threshold, ensuring stable switching without causing current vector sudden changes or over-current conditions.
Solution Approach 2:
The system uses feedback by continuously monitoring the angle error between command and estimated rotor positions. This feedback mechanism determines when the transition conditions are met, allowing the system to switch from open loop to closed loop operation at the optimal moment, thereby maintaining stability while improving control accuracy.
2Measurement precision
If sensors are directly attached to the motor for position and speed feedback, then the control precision is improved, but the motor performance and reliability deteriorate
Solution Approach 1:
The system replaces mechanical sensors with an electronic estimation mechanism. Instead of using physical sensors that require mechanical attachment to the motor, the system estimates rotor position and speed through mathematical algorithms and electrical measurements, thereby maintaining high measurement precision while eliminating the reliability issues associated with mechanical sensor attachment.
3Manufacturing precision
If the current vector is changed during coordinate system transition, then the control accuracy is improved, but torque ripple and over-current occur
Solution Approach 1:
The system performs preliminary verification by checking whether the angle error is within the predetermined threshold before executing the coordinate system transition. This preliminary action ensures that the transition occurs only under stable conditions, preventing torque ripple and over-current while maintaining control precision.
Solution Approach 2:
The system applies preliminary anti-action by establishing a precondition (angle error within threshold) that prevents harmful effects. By ensuring the angle error is minimal before transitioning, the system preemptively avoids the generation of torque ripple and over-current that would otherwise occur during unstable transitions.
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.