Feedforward Control of PMDC Motors Using Back-EMF Compensation
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Solution Overview
Problem
Feedforward current and torque control of permanent magnet DC (PMDC) motors face limitations in bandwidth and disturbance rejection due to the need for accurate machine models and lack of noise resilience, especially in applications like electric power steering (EPS) systems where cost-effective and stable control is essential.
Innovation Solution
A motor control system employing feedforward control computes voltage commands based on input torque signals, brush drop voltage, and back-EMF drop voltage, summing these to generate output torque without requiring current sensors, thereby enhancing control performance and stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If feedforward control is used to eliminate current sensors and reduce noise, then device complexity and noise are reduced, but control bandwidth and disturbance rejection performance deteriorate
Solution Approach 1:
The patent implements a hybrid control system that combines feedforward control with feedback mechanisms. Specifically, it uses feedback from position and velocity measurements to compensate for the limitations of open-loop feedforward control, thereby maintaining high control bandwidth and disturbance rejection while still eliminating the need for current sensors. The feedback loop continuously adjusts the control signals based on actual motor performance.
Solution Approach 2:
The system dynamically adjusts control parameters such as voltage commands and current references based on operating conditions. By changing parameters like PWM duty cycle, switching frequency, and control gains adaptively, the system optimizes both bandwidth and disturbance rejection performance while maintaining sensorless operation.
2Device complexity
If feedforward control with accurate machine models is used, then current sensor requirements are eliminated, but manufacturing precision and model accuracy requirements increase
Solution Approach 1:
The system performs self-identification and adaptive tuning of motor parameters during operation. It automatically identifies motor characteristics such as resistance, inductance, and back-EMF constants, and adapts the control model accordingly. This eliminates the need for highly precise manual modeling while maintaining accurate control performance.
Solution Approach 2:
The system performs preliminary parameter identification and model calibration during motor commissioning or idle periods before normal operation begins. This preliminary action establishes accurate machine models in advance, reducing the need for continuous high-precision modeling during operation and simplifying the overall control implementation.
3Speed
If feedback control is used to improve bandwidth and disturbance rejection, then control performance is enhanced, but device complexity increases due to current sensor requirements
Solution Approach 1:
The system uses position and velocity sensors as intermediaries to indirectly obtain current information needed for feedback control. By measuring mechanical parameters and using motor models to infer electrical states, the system achieves feedback control performance without directly measuring current, thus avoiding the complexity and cost of current sensors.
4Object-affected harmful factors
If feedforward control is used to reduce noise transmission, then noise immunity is improved, but disturbance rejection performance worsens
Solution Approach 1:
The hybrid control system uses feedback from position and velocity measurements to detect and compensate for disturbances in real-time. This feedback mechanism maintains strong disturbance rejection performance while the feedforward component keeps noise transmission low by using open-loop voltage control based on desired torque or position trajectories.
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 improves torque control bandwidth, reduces instability, and provides cost-effective, fault-tolerant control for PMDC motors in applications like EPS systems by utilizing estimated motor velocity and disturbance compensation, achieving comparable dynamic performance to feedback control systems.
Implementation Method 1
Permanent Magnet DC (PMDC) motors are widely employed for motion control applications
Implementation Method 2
computing a second voltage command for the motor based on a brush drop voltage of the motor and a back-EMF drop voltage of the motor
Data Source
AI summary
Technical solutions are described for a motor control system that includes a feedforward control module to control an output torque generated by the motor. The feedforward controlling includes computing a first voltage command for the motor based on an input torque signal. Further, the feedforward controlling includes computing a second voltage command for the motor based on a brush drop voltage of the motor and a back-EMF drop voltage of the motor. Further, feedforward controlling includes computing a voltage command for the motor by summing the first voltage command and the second voltage command. Further yet, the feedforward controlling includes sending the voltage command to the motor for generating the output torque.