Electric Motor Offset Angle Calibration via Constant-Torque Current Variation
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Solution Overview
Problem
Existing methods for calibrating the offset angle in field-oriented control of electric machines are inaccurate and require mechanical measures or complex machine models, affecting torque control and vehicle performance.
Innovation Solution
A method that periodically varies the current vector along a line of constant torque in the d/q coordinate system to ascertain the speed signal and calibrate the offset angle, allowing for precise calibration during normal vehicle operation without relying on machine-specific data or mechanical components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If existing calibration methods are used, then mechanical measures or complex machine models are required, but calibration accuracy is poor and device complexity increases
Solution Approach 1:
The patent replaces mechanical calibration measures with an electrical control method. By periodically varying the current vector in the d/q coordinate system and measuring the resulting speed oscillations, the offset angle is calibrated through electrical signal processing rather than mechanical adjustments, thereby improving accuracy while reducing mechanical complexity
Solution Approach 2:
The patent changes the control parameters by periodically varying the current vector amplitude and/or direction in the d/q coordinate system. This parameter variation creates measurable speed oscillations that depend on the offset angle, enabling accurate calibration through parameter-based measurement rather than complex mechanical or modeling approaches
2Manufacturing precision
If existing calibration methods are used, then complex machine models are required, but calibration accuracy is poor and manufacturing precision is affected
Solution Approach 1:
The calibration method uses the electric machine's own operational characteristics (speed response to current vector variation) to determine the offset angle. The machine serves its own calibration needs by providing the speed signal that reveals the offset error, eliminating dependence on external complex machine models and improving both calibration accuracy and torque control precision
3Measurement precision
If offset angle calibration is performed, then torque oscillations occur during calibration, but high accuracy calibration is achieved
Solution Approach 1:
The patent applies periodic variation to the current vector during calibration. This periodic action creates controlled, periodic speed oscillations that can be measured and used to determine the offset angle. The periodic nature allows for systematic measurement while the oscillations remain bounded and controllable, achieving accurate calibration with manageable torque variations
4Productivity
If calibration is performed during normal operation, then vehicle performance is maintained, but driver perception of maladjustments may occur
Solution Approach 1:
The patent applies partial action by introducing small periodic variations in the current vector rather than large changes. This partial variation creates minimal speed oscillations that are sufficient for accurate offset angle measurement while remaining below the threshold of driver perception, allowing calibration during normal operation without affecting vehicle performance or driver comfort
Data Source
AI summary
A method (100) for calibrating an offset angle (PhiO) for field-oriented control of an electric machine (210) between an angle signal (W) of a position encoder (220) and the direction of the rotor flux (RF), having the steps of: periodically varying (120) a current vector (Is) along a line of constant torque; ascertaining (130) a speed signal (n_t) of the position encoder (220) of the electric machine (210); calibrating (140) the offset angle (PhiO) on the basis of the ascertained speed signal (n_t).