Permanent Magnet Motor Angle Offset Calibration Using Direct-Axis Voltage
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Solution Overview
Problem
Angular position sensing offsets in permanent magnet synchronous motors used in electric vehicles can reduce torque generation efficiency and overall motor control stability due to mechanical variations and tolerances, affecting the accuracy of angular position information provided by sensors.
Innovation Solution
A method involving direct-axis voltage measurement and comparison with a reference voltage, using a proportional integral controller to iteratively adjust the angle offset estimate until the measured direct-axis voltage equals the reference voltage, thereby calibrating the angular position sensor and improving torque generation efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If angular position sensor is used to determine rotor position, then motor control capability is improved, but angular offset between sensor reading and actual magnetic axis reduces torque generation efficiency
Solution Approach 1:
The patent employs feedback by measuring the direct-axis voltage during motor operation and using this measurement to iteratively adjust the angle offset estimate. The proportional integral controller continuously compares the measured direct-axis voltage with a reference voltage and adjusts the offset until convergence, creating a closed-loop feedback system that eliminates angular offset errors and maximizes torque generation efficiency.
Solution Approach 2:
The patent changes the electrical parameter (direct-axis voltage) to diagnose and correct the angular offset issue. By measuring the direct-axis voltage and using it as a feedback signal to adjust the angle offset parameter, the system dynamically modifies control parameters to maintain optimal torque generation efficiency despite sensor inaccuracies.
2Productivity
If angle offset is adjusted to compensate for sensor inaccuracy, then torque generation efficiency is improved, but measurement precision of angular position sensor becomes critical
Solution Approach 1:
The feedback mechanism measures the direct-axis voltage as an indicator of angular offset accuracy. By continuously monitoring this voltage and adjusting the offset estimate accordingly, the system compensates for sensor measurement errors and maintains high torque generation efficiency even when the angular position sensor has inherent inaccuracies.
Solution Approach 2:
The patent replaces reliance on direct mechanical/angular measurement with an electrical measurement approach. Instead of depending solely on the angular position sensor's mechanical reading, the system uses electrical measurements (direct-axis voltage) to infer and correct angular offset, substituting electrical sensing for mechanical sensing to achieve higher effective precision.
3Measurement precision
If direct-axis voltage measurement is used for calibration, then angle offset accuracy is improved, but device complexity increases due to additional measurement and control requirements
Solution Approach 1:
The patent achieves multi-functionality by using the existing motor control infrastructure to perform both motor control and angle offset calibration. The same proportional integral controller and voltage measurement systems used for motor operation are leveraged for calibration purposes, eliminating the need for separate dedicated calibration hardware and reducing overall device complexity.
Solution Approach 2:
The system performs self-calibration by using its own operational data (direct-axis voltage measurements during normal operation) to automatically adjust and correct its angular offset parameters. The motor control system serves its own calibration needs without requiring external intervention or separate calibration equipment, thereby avoiding additional complexity.
Data Source
AI summary
In a general aspect, a method includes measuring, for a permanent magnet motor having a rotor rotating at a speed, a direct-axis voltage in a rotor frame of reference. The speed is determined by an angular position sensor. The method further includes comparing the measured direct-axis voltage with a reference voltage, and determining, based on the comparing, an angle offset estimate of the angular position sensor. The method also includes iteratively adjusting the angle offset estimate until the measured direct-axis voltage substantially equals the reference voltage.