DC Motor Speed Estimation Using Back-EMF in MDPS
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Solution Overview
Problem
Conventional MDPS systems using DC motors without position sensors face challenges in accurately estimating motor speed due to the reliance on low-pass filter analog circuits, which incur additional costs and are sensitive to pass band settings. Additionally, speed estimation errors increase in situations with rapid changes in current and voltage.
Innovation Solution
An apparatus and method for estimating DC motor speed in an MDPS system, utilizing a motor speed estimator that calculates motor speed based on DC link voltage, motor current, and voltage command, without the need for a voltage measurement circuit. This involves calculating dead time voltage, motor resistance voltage, and motor inductance voltage to accurately determine motor speed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a low-pass filter analog circuit is used to measure voltage across the motor, then voltage measurement is achieved, but manufacturing cost increases and measurement precision becomes sensitive to pass band settings
Solution Approach 1:
The patent replaces the analog low-pass filter circuit with a digital signal processing approach. The voltage measurement function is achieved through digital filtering and calculation algorithms implemented in the controller, eliminating the need for complex analog voltage measurement circuits while maintaining measurement precision.
Solution Approach 2:
The patent introduces intermediate calculation steps including dead time voltage calculation and motor resistance voltage calculation as mediators between the raw voltage command and the final speed estimation. These intermediate variables serve as digital proxies that eliminate the need for direct analog voltage measurement circuits.
2Productivity
If conventional speed-voltage-current relation equation is used for speed estimation, then speed estimation is achieved, but measurement precision deteriorates in sections where current and voltage are rapidly changed
Solution Approach 1:
The patent performs preliminary calculations of dead time voltage and motor resistance voltage before computing the final speed estimation. By pre-calculating these intermediate values and accounting for dead time effects in advance, the system compensates for rapid changes in current and voltage, improving speed estimation accuracy during dynamic conditions.
Solution Approach 2:
The patent changes the estimation approach by introducing dead time voltage compensation and motor resistance voltage calculation as additional parameters. This modifies the conventional speed-voltage-current relation to account for dynamic effects, improving precision during rapid transitions.
3Measurement precision
If pass band settings are changed to improve measurement accuracy, then measurement precision improves, but device complexity increases due to circuit modification requirements
Solution Approach 1:
The patent implements a dynamic estimation approach that adapts to various operation situations through software-based calculations rather than fixed analog circuit parameters. The dead time voltage compensation and motor resistance voltage calculation automatically adjust to different operating conditions, providing both high precision and versatility without requiring circuit modifications.
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
The proposed solution reduces costs by eliminating the need for a voltage measurement circuit and enhances the accuracy of motor speed estimation by considering dynamic motor states and dead time voltage, thereby improving the system's ability to handle various operating conditions.
Implementation Method 1
calculating the motor speed based on the dead time voltage, the voltage command, the motor resistance voltage, the motor inductance voltage, and a preset motor counter electro-motive force constant
Data Source
AI summary
An apparatus with motor speed estimation includes: a motor speed estimator configured to estimate a motor speed based on a DC link voltage for driving a motor, a motor current flowing through the motor, and a voltage command; and a limiter configured to generate a current command based on the estimated motor speed, a torque command, and the DC link voltage.