Adaptive Cogging Torque Compensation in Permanent Magnet Machines
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Solution Overview
Problem
Existing methods for reducing cogging torque in permanent magnet machines are inadequate as they fail to adapt to varying speed and load conditions, leading to residual torque variations and vibrations.
Innovation Solution
An adaptive method involving measurement of rotor position and speed, running tests with different compensation signals, and calculating complex cogging compensation amplitudes to apply a dynamic torque correction based on vibration analysis, allowing for real-time adjustment of compensation signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If static compensation software with constant amplitudes and phases is used, then compensation works fine for a specific load and speed, but it fails when speed and load differ much from tuning conditions
Solution Approach 1:
The patent transforms the static compensation approach into a dynamic one by continuously adapting the compensation signal parameters (amplitudes and phases) based on real-time measurements of actual cogging torque. The system uses feedback from position and speed sensors to update compensation parameters dynamically, ensuring effectiveness across varying operating conditions rather than being limited to fixed tuning points
Solution Approach 2:
The patent implements a feedback mechanism where the actual cogging torque is measured using position and speed sensors, and this measured information is fed back to continuously adjust the compensation signal parameters. The system calculates the actual cogging torque from measured position and speed, then uses this feedback to adaptively tune the compensation amplitudes and phases, creating a closed-loop control system that maintains reliability across different operating conditions
2Object-generated harmful factors
If skewed magnets or stator slots are used to minimize cogging torque, then residual cogging torque is reduced, but individual differences in cogging torque characteristics remain large between identical machines
Solution Approach 1:
The patent enables each motor to self-adjust its compensation parameters based on its own measured cogging torque characteristics. By using feedback from position and speed sensors, each motor independently determines its actual cogging torque profile and adapts its compensation signal accordingly, eliminating the need for manual tuning and ensuring consistent performance across identical machines despite manufacturing variations
Solution Approach 2:
The patent changes the approach from fixed mechanical design parameters (skew angles, slot configurations) to adjustable electrical compensation parameters (amplitudes and phases of compensation signals). This allows the system to adapt the compensation parameters to match the actual measured cogging torque characteristics of each specific motor, thereby reducing individual differences between identical machines
3Adaptability or versatility
If adaptive compensation with continuous parameter adjustment is implemented, then compensation effectiveness improves across varying conditions, but system complexity increases
Solution Approach 1:
The patent makes the existing feedback control infrastructure multi-functional by using the same position and speed sensors already present for basic motor control to also measure cogging torque and enable adaptive compensation. This approach achieves adaptability without adding dedicated hardware, as the control system simultaneously performs both basic speed/torque control and adaptive cogging compensation using the same sensor inputs
Data Source
AI summary
A method for reducing cogging torque effects of an electrical permanent magnet machine includes running an “a” test and a “b” test with different cogging compensation signals. A first value is calculated by multiplying a complex cogging amplitude of the compensation signal applied for the “a” test with a complex amplitude of a vibration signal resulting from cogging torque of the “b” test. A second value is calculated by multiplying a complex cogging amplitude of the compensation signal applied for the “b” test with a complex amplitude of the vibration signal resulting from cogging torque of the “a” test. A desired complex cogging compensation amplitude is calculated by dividing the difference between the first and second values by a difference between the complex amplitudes of the vibration signals resulting from the “b” test and the “a” test. A cogging compensation torque is applied to the machine based on the desired complex cogging compensation amplitude.