Electric Motor Rotor Position Offset Calibration
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Solution Overview
Problem
Existing methods for calibrating the rotor position offset of electric motors, such as IPM motors, are impractical for field calibration during normal vehicle operation due to the need for auxiliary motors and complex torque component alignments.
Innovation Solution
A system and method utilizing an electronic data processing system coupled with sensors and an inverter circuit to apply controlled current commands, determining the rotor position offset by measuring the difference between enforced and fake rotor positions, allowing for field calibration without auxiliary motors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If back electromotive force (EMF) measurements are used to calibrate motor position, then calibration accuracy can be improved, but an auxiliary motor is required to rotate the shaft which increases device complexity and is not practical for field calibration
Solution Approach 1:
The patent extracts the calibration function from the traditional EMF measurement method that requires an auxiliary motor. Instead of using back EMF measurements during rotation, the invention applies voltage pulses directly to the motor windings and measures the resulting current responses to determine rotor position offset, completely removing the need for an auxiliary motor while maintaining calibration accuracy
Solution Approach 2:
The patent replaces the mechanical rotation system (auxiliary motor rotating the shaft) with an electrical measurement system. By applying voltage pulses and measuring current responses, the system determines rotor position without mechanical rotation, substituting a mechanical calibration approach with an electrical one that is suitable for field calibration during normal vehicle operation
2Power
If IPM motor rotor alignment scheme is used with magnetic torque and reluctance torque components along different axes, then motor performance is improved, but rotor position calibration becomes more difficult due to torque component misalignment
Solution Approach 1:
The patent introduces an intermediary measurement approach using voltage pulses and current responses as a mediator between the control system and the rotor position. Instead of directly measuring torque components or using complex alignment schemes, the system applies voltage pulses to the windings and uses the resulting current measurements to indirectly determine the rotor position offset, simplifying the calibration process while maintaining IPM motor performance
Solution Approach 2:
The patent changes the measurement parameters from torque-based measurements to electrical parameter-based measurements. By measuring voltage and current responses instead of torque components, the system determines rotor position without being affected by the misalignment between magnetic torque and reluctance torque components, making calibration easier while preserving the performance benefits of IPM motors
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
Enables accurate and practical field calibration of rotor position offset in electric motors, improving motor control performance and ensuring robust controllability by compensating for torque component misalignments.
Implementation Method 1
applying a zero direct-axis current command and positive and negative quadrature-axis current commands sequentially to a motor to move a rotor to an enforced position
Implementation Method 2
calibrating a motor with back electromotive force (EMF) measurements
Data Source
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AI summary
While enforcing a fake position in the data processing system (120) and applying a zero direct-axis current command, positive and negative quadrature-axis current commands are applied sequentially and at approximately same magnitude to urge the rotor toward an enforced position. A processing module (116) measures a positive quadrature-axis current aligned raw position data after application of the positive quadrature-axis current command and measures negative quadrature-axis current aligned raw position data for the rotor after application of the negative quadrature-axis command. An initial position offset calibrator (151) or data processor determines a difference between the raw position data to determine an alignment of a true averaging axis. An initial position offset calibrator (151) or data processor determines a raw averaging axis position data based on an average of the raw position data.