Rotor Position Offset Calibration Using Torque Zero Crossing
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Solution Overview
Problem
Electrical machines face inaccuracies in determining the angular position of rotors due to motor sensor offsets, which can lead to misalignment and reduced precision in angular displacement measurements.
Innovation Solution
A method involving the application of electrical current to stator windings to measure torque values at specific angular positions, approximating a line between these values, and using bi-section search techniques to determine the angular offset where torque is zero, thereby calibrating the actual rotor position relative to the motor sensor indication.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a motor sensor is used to monitor rotor angular position, then rotor position can be determined, but the measurement precision is reduced due to offset errors
Solution Approach 1:
The patent replaces the motor sensor-based mechanical/electrical measurement system with a torque-based physical measurement system. By measuring torque at different angular positions and using the torque-zero point to determine actual rotor position, the system eliminates sensor offset errors entirely, achieving high precision without relying on potentially inaccurate sensor indications
Solution Approach 2:
The system uses the electrical machine's own torque characteristics to determine rotor position. The torque measurement and zero-crossing detection process allows the machine to self-calibrate and determine its actual rotor position without external reference or additional sensing components, making the system self-sufficient and highly accurate
2Loss of time
If traditional calibration methods are used, then rotor position offset can be determined, but the calibration process is time-consuming and requires prior knowledge of the electrical machine
Solution Approach 1:
The patent implements preliminary action by establishing a torque-based calibration methodology that can be applied universally without requiring prior knowledge of specific machine characteristics. The method pre-defines the torque measurement approach and zero-crossing detection algorithm, allowing rapid calibration across different electrical machine types without extensive setup or machine-specific programming
Solution Approach 2:
The system changes the calibration approach from sensor-based angular position reading to torque-based physical measurement. By varying the stator winding currents to generate measurable torque at different angular positions, and detecting the zero-torque point, the system transforms the calibration problem into a more direct and faster physical measurement that eliminates complex sensor calibration procedures
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 accurately determines and stores the angular offset, enhancing the precision of rotor position measurements and allowing for quicker calibration without prior knowledge of the electrical machine, improving operational accuracy and efficiency.
Implementation Method 1
Electrical machines (also referred to as electric motors) include stators having a plurality of windings and rotors that are angularly displaced relative to the stator in response to the application of electrical current to the windings through induction
Data Source
AI summary
A method of calibrating an electrical machine to determine an angular offset between a motor sensor indicated position and an actual rotor position, including the steps of: supplying electrical current to stator windings; identifying a quadrant of a rotor where a rotor pole is located; approximating a line between a torque value measured at a lower angular boundary of the identified quadrant and a torque value measured at an upper angular boundary of the identified quadrant; and determining an angular offset by locating an angular position where torque exerted by the rotor is zero.