Electric Generator Cogging Torque Compensation via Current Injection
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Solution Overview
Problem
Existing methods for reducing cogging torque in electric generators, particularly in low-speed applications like wind turbines, face inaccuracies in prediction and difficulties in measurement due to material variations and mechanical resonance, requiring high-cost and high-bandwidth sensors.
Innovation Solution
Estimating cogging torque by determining a compensating current through iterative test runs, allowing for compensation across varying operating conditions using lower-cost sensors and mathematical modeling, and applying this current to minimize torque ripple.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If cogging torque is measured using a specially designed test rig with torque transducers, then measurement accuracy can be improved, but device complexity and cost increase due to high-bandwidth sensors and constant low-speed rotation requirements
Solution Approach 1:
The patent replaces mechanical torque measurement systems with an electrical measurement approach. Instead of using mechanical torque transducers and test rigs, the method measures cogging torque by analyzing electrical currents in the generator windings during a test run. The control unit determines cogging torque values by processing electrical signals from the generator, eliminating the need for complex mechanical measurement equipment while maintaining measurement accuracy.
2Device complexity
If prediction methods like finite elements method are used to determine cogging torque, then device complexity is reduced, but manufacturing precision deteriorates due to big errors from material variation and tolerance
Solution Approach 1:
The patent implements a feedback-based measurement and compensation system. During a test run, the control unit measures the actual electrical currents in the generator windings and uses this feedback information to calculate the actual cogging torque values present in the specific generator unit. This feedback approach accounts for material variations and manufacturing tolerances by measuring the actual performance of the specific generator rather than relying on theoretical predictions, thereby improving accuracy while keeping the system simple.
3Measurement precision
If test run is conducted at low rotating speed to accurately measure cogging torque, then measurement precision improves, but productivity decreases due to difficulty in maintaining constant speed and mechanical resonance
Solution Approach 1:
The patent replaces mechanical speed control requirements with an electrical measurement system that can operate across varying speeds. Instead of requiring the generator to rotate at a constant low speed using mechanical prime movers, the method measures electrical currents during a test run and calculates cogging torque values that can then be applied across the entire operating speed range. This substitution eliminates the need for precise mechanical speed control while maintaining measurement accuracy and improving test efficiency.
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 effectively reduces cogging torque ripple with lower-cost sensors and improved accuracy, enabling efficient operation across different speeds and loads, and can be adapted for various generator conditions.
Implementation Method 1
an electric generator operable according to the inventive method and a wind turbine comprising such an electric generator
Implementation Method 2
Cogging torque is an undesirable effect present in electrical motors or generators which is caused by the position dependent interaction between the rotor and the stator of the electric machine
Data Source
Figure 1~2
AI summary
A method of controlling an electric generator is provided. While rotating the electric generator at a known rotating speed, a cogging torque signal representative of a cogging torque of the electric generator such as torque, vibration or acoustic noise is measured. Then a compensating current having a predetermined current characteristic is injected into the electric generator. This is repeated for a plurality of different predetermined current characteristics until the measured cogging torque signal meets a predetermined condition. One of the predetermined current characteristics is selected as a base operating current characteristic. The electric generator will be operated injecting an operating compensating current having an operating current characteristic derived from the base operating current characteristic in accordance with an operating state of the electric generator. Further aspects of the invention relate to an electric generator operable according to the invention and a wind turbine comprising such an electric generator.