Motor Position Calibration via Back-EMF Zero-Crossing
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Solution Overview
Problem
Existing methods for determining the electrical angle offset of motor position sensors in vehicular electric motors, such as those used in EPAS systems, are time-consuming and require costly calibration due to manufacturing tolerances, leading to alignment errors that need to be corrected during end-of-line calibration.
Innovation Solution
A method involving rotating the motor using an external drive system, measuring and converting motor phase voltages to a DQ reference frame to calculate the electrical angle offset, which eliminates the need for compensation tables and reduces calibration time, and includes normalization to motor velocity and removal of DC offsets to improve accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If traditional calibration methods are used to determine electrical angle offset, then alignment accuracy can be improved, but calibration time and manufacturing cost increase significantly
Solution Approach 1:
The patent extracts the back-EMF signal from the motor operation and uses it directly for angle offset determination. By measuring the back-EMF voltage during normal motor operation and processing it through coordinate transformation and zero-crossing detection, the method obtains alignment information without requiring separate calibration procedures, thus eliminating time loss while maintaining accuracy
Solution Approach 2:
The motor's own back-EMF signal is used to determine its alignment characteristics. The system serves itself by using the voltage generated during normal operation to automatically calculate the electrical angle offset, eliminating the need for external calibration equipment and procedures, thereby reducing both time and cost
2Manufacturing precision
If Q-axis voltage method is used to calibrate motor position, then alignment accuracy is improved, but the calibration process becomes highly time-consuming
Solution Approach 1:
The patent utilizes the periodic nature of back-EMF signals in multi-phase motors. By analyzing the periodic voltage waveforms generated during motor operation and detecting their zero-crossing points, the system determines angle offset information continuously during normal operation rather than requiring separate calibration cycles, thus maintaining high calibration speed
Solution Approach 2:
The calibration process is integrated into normal motor operation. The back-EMF measurement and angle offset calculation continue during motor running without interrupting useful work, allowing calibration to occur continuously rather than in discrete time-consuming steps, thereby maintaining high productivity
3Loss of time
If mapping tables are created for each motor variant to correct speed asymmetry, then calibration time per motor is reduced, but the overall process becomes more complex and requires updates for each variant
Solution Approach 1:
The patent determines angle offset by detecting the zero-crossing point of the back-EMF signal, which directly reflects the electrical position. By changing the approach from using pre-created mapping tables to directly measuring the electrical angle through back-EMF zero-crossing detection, the system eliminates the need to manage complex variant-specific tables while maintaining accuracy for all motor types
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 method allows for quicker determination of the electrical angle offset for each motor individually, reducing time and effort, and provides a more accurate alignment without the need for extensive calibration processes, while also measuring back-EMF for further calculations.
Implementation Method 1
measuring a motor phase voltage of each phase of the multi-phase electric motor, the motor phase voltage comprising a back-EMF generated by the rotation of the motor
Data Source
AI summary
A method of determining an electrical angle offset of a motor position sensor mounted to a multi-phase electric motor, the method comprising rotating a rotor of the multi-phase electric motor at a motor velocity using an external drive system, measuring a motor phase voltage of each phase of the multi-phase electric motor, the motor phase voltage comprising a back-EMF generated by the rotation of the motor, converting the motor phase voltage to a DQ reference frame to form a DQ motor phase voltage and calculating the electrical angle offset from the DQ motor phase voltages.