Motor Control Circuit Adaptive Mode Switching for RPM Overshoot
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Solution Overview
Problem
Existing motor control systems using proportional-integral (PI) control for feedback control of motor RPM often result in overshoot and undershoot during acceleration and deceleration, which are not effectively managed, especially when the target RPM changes discontinuously.
Innovation Solution
A control circuit that switches between a first mode with a monotonically changing control command and a second mode using PI control, based on the ratio of actual to target RPM, to adaptively suppress overshoot and undershoot, featuring a cycle counter, controller, ramp waveform generator, PI controller, and mode selector.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If PI control is used for feedback control of motor RPM, then the motor speed can be controlled to approach target value, but overshoot and undershoot occur during acceleration and deceleration
Solution Approach 1:
The control mode is dynamically switched between open-loop and closed-loop based on the ratio of actual RPM to target RPM. When the ratio indicates proximity to target (within threshold), closed-loop PI control is activated; otherwise, open-loop control is used. This dynamic adaptation prevents overshoot/undershoot while maintaining accuracy.
Solution Approach 2:
The system uses feedback from the RPM detection value to determine when to switch to closed-loop control mode. The switching decision is based on comparing the ratio of actual to target RPM against a threshold, enabling feedback-driven mode transition that optimizes both stability and precision.
2Stability of the object's composition
If continuous changing of target RPM is implemented to avoid discontinuity during switching, then RPM stability improves, but the control system complexity increases
Solution Approach 1:
A mode switching mechanism acts as an intermediary between open-loop and closed-loop control systems. This intermediary selectively activates the appropriate control mode based on RPM proximity to target, avoiding the need for continuous target RPM adjustment while maintaining stability.
Solution Approach 2:
The control process is segmented into distinct phases: open-loop control for coarse speed adjustment and closed-loop PI control for fine-tuned precision near the target. This segmentation allows each control mode to operate in its optimal range without requiring complex continuous adjustment mechanisms.
3Ease of operation
If open loop control is used to apply drive voltage corresponding to target RPM, then control simplicity is maintained, but RPM accuracy and ability to suppress overshoot/undershoot deteriorates
Solution Approach 1:
The control system dynamically transitions from simple open-loop control to precise closed-loop PI control based on the ratio of actual to target RPM. This dynamic switching maintains simplicity during coarse adjustment while achieving high accuracy near the target without requiring complex continuous control mechanisms.
Data Source
AI summary
A control circuit includes: a cycle counter configured to measure a cycle of revolutions per minute (RPM) signal indicating an RPM of a motor to be driven to generate a digital measurement value; and a controller configured to generate a control command based on a digital target value corresponding to a target cycle of the RPM signal and the measurement value, wherein the controller switches between a first mode in which the control command is monotonously changed and a second mode in which the control command is generated based on proportional-integral (PI) control.