Electric Motor Position Control with Disturbance Observer and Rate Limiter
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Solution Overview
Problem
Existing position control devices for electric motors face challenges in achieving high response and stability due to torque limitations, leading to vibration and overshooting phenomena, making it difficult to maintain high feedback control and response frequency.
Innovation Solution
The implementation of a position control device with a disturbance observer, rate-of-change limitation section, and target value filter, which estimates disturbance torque and sets upper and lower limits for rate-of-change and angular velocity to prevent overshoot, along with a low-pass filter to stabilize the output.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If torque limit is imposed in the speed control section, then the electric motor operates within its torque range, but the position control response becomes slow and windup phenomenon occurs
Solution Approach 1:
The rate of change limiter proactively limits the angular velocity command before it can cause windup, and the disturbance observer anticipates and compensates for disturbances in advance. This preliminary action prevents the accumulation of large errors that would otherwise slow down the position control response when torque limits are reached.
Solution Approach 2:
The rate of change limiter acts as an intermediary between the position control section and speed control section, modifying the angular velocity command to prevent excessive torque demands. This intermediary component allows the system to maintain high response characteristics while ensuring torque limits are not violated, resolving the contradiction between response speed and torque compliance.
2Speed
If high response position control is implemented, then the feedback control frequency can be increased, but vibration and overshooting occur due to torque limitations
Solution Approach 1:
The disturbance observer continuously monitors the difference between the actual motor torque and the commanded torque, using this feedback to estimate disturbance torque in real-time. This feedback mechanism allows the system to maintain high control frequency while compensating for disturbances that would otherwise cause vibration and overshoot under torque constraints.
Solution Approach 2:
The rate of change limiter dynamically adjusts the angular velocity command based on the estimated disturbance torque, changing the control parameters adaptively. When disturbances are detected, the limiter reduces the rate of change of angular velocity to prevent overshoot, while allowing high-frequency response when conditions permit, thus resolving the contradiction between response speed and stability.
3Manufacturing precision
If rate of change limitation is applied to prevent overshoot, then position accuracy improves, but the control system complexity increases
Solution Approach 1:
The rate of change limiter and disturbance observer are integrated into the existing position-control device architecture, combining multiple functions (disturbance estimation, rate limiting, and position control) into a unified control system. This merging approach improves position accuracy while minimizing the increase in system complexity by reusing existing computational resources and control structures.
Data Source
AI summary
Position control device for electric motor inputs deviation signal between angle command and angle detection value to position control section and calculates angular velocity command, inputs deviation signal between this angular velocity command and angular velocity detection value to speed control section and calculates torque current command, and controls, according to this torque current command, the electric motor current control section. The Position control device has disturbance observer section which inputs the torque current command and the angular velocity detection value and estimates signal corresponding to disturbance torque; rate-of-change limitation section which has limiter inputting disturbance observer output value by this disturbance observer section and performing rate-of-change limitation of upper and lower limit values of the angle command; and target value filter section which is configured by control gain equivalent to the speed control section and through which the angular velocity command from the position control section passes.