Brushed Motor Velocity Estimation via State Observer
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Solution Overview
Problem
Existing electric power steering (EPS) systems face challenges in accurately estimating motor velocity without direct measurement, leading to noise, delay, and instability due to the difficulty in obtaining accurate motor parameters, especially for brushed motors, which affects steering feel and control performance.
Innovation Solution
A state observer module with a proportional-integral-derivative (PID) controller and lowpass filter is used to estimate motor velocity, incorporating a compensator that converges the estimated position with the measured position, and a motor-velocity based lowpass filter module to improve estimation accuracy and reduce noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If direct measurement using sensors and tachometers is used to obtain motor velocity, then measurement precision is improved, but device complexity and cost increase
Solution Approach 1:
The patent creates a virtual copy of the motor system through a state observer module that replicates motor dynamics using mathematical models. This software-based copy estimates velocity, position, and other states without requiring physical sensors, thereby reducing hardware complexity while maintaining measurement precision through accurate state reconstruction from available measurements
Solution Approach 2:
The patent replaces mechanical measurement systems (sensors and tachometers) with an electronic/software-based state observer. The observer uses electrical measurements and mathematical models to substitute for mechanical velocity sensing, eliminating the need for additional hardware components while providing accurate velocity estimation
2Ease of operation
If differential of position signal is used to generate motor velocity, then ease of operation is improved, but measurement precision deteriorates due to noise and delay
Solution Approach 1:
The patent implements a feedback mechanism where the state observer continuously compares estimated states with actual measurements and adjusts estimates accordingly. The compensator uses feedback from position error to correct velocity and position estimates, eliminating the noise and delay problems associated with simple differentiation while maintaining ease of operation
Solution Approach 2:
The patent introduces a state observer module as an intermediary between position measurements and velocity output. This intermediary processes position signals through mathematical models and feedback mechanisms rather than direct differentiation, filtering out noise and delay while still providing easy velocity generation from position data
3Device complexity
If electrical behaviors of motor are used to model motor system, then device complexity is reduced, but measurement precision deteriorates due to difficulty in obtaining proper parameter values
Solution Approach 1:
The patent implements a self-tuning mechanism where the state observer automatically adapts to the specific motor parameters through feedback from actual system behavior. The compensator adjusts model parameters based on observed position errors, allowing the system to self-calibrate and achieve accurate velocity estimation without requiring manual parameter identification or complex setup procedures
Solution Approach 2:
The patent uses parameter adaptation where the state observer model parameters are adjusted based on actual system performance. The compensator modifies effective parameters like brush drop voltage and inertia based on observed behavior, allowing the simple electrical model to achieve high precision by dynamically adapting parameters rather than requiring fixed accurate values
4Device complexity
If brush drop voltage is not properly obtained in the model, then device complexity is reduced, but measurement precision deteriorates causing offset from zero velocity
Solution Approach 1:
The patent uses feedback from position measurements to compensate for inaccurate brush drop voltage parameters. The compensator detects position errors that arise from parameter inaccuracies and generates corrective signals that eliminate the resulting velocity offset, allowing accurate zero velocity detection without precise brush drop voltage measurement
Solution Approach 2:
The state observer acts as an intermediary that isolates the system from parameter uncertainties. By using feedback compensation, the observer mediates between imperfect parameter knowledge and accurate velocity estimation, preventing parameter errors from directly affecting measurement precision while keeping the system simple
Data Source
AI summary
A motor control system of a motor is provided. The system includes a state estimation observer that computes an estimated velocity based on an inertia-damping response to the dynamics of the motor shaft, a torque command signal, and the compensated command signal. This compensated signal comes from a proportional-integral-derivative (PID) controller that determines a difference between a sensed position and an estimated position. The estimated position is determined by the estimated velocity and an integrator. The control system may also include a motor-velocity based lowpass filter which applies a filter to the estimated velocity.