Electrical Machine Airgap Control via Negative Id Current Injection
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Solution Overview
Problem
Large electrical machines, such as wind turbine generators, face challenges in maintaining a uniform airgap width due to manufacturing tolerances, temperature differences, and eccentricity, which can lead to magnetic force imbalances and reduced efficiency, necessitating either down-regulation or a wider airgap that compromises electromagnetic performance.
Innovation Solution
A method that measures airgap width during operation and injects a corrective negative Id current to maintain the airgap width above a critical minimum, using direct-quadrature-zero (dq0) transformation to determine and apply the necessary current to the windings, thereby preventing critical narrowing and maintaining efficient operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the airgap width is reduced to improve electromagnetic performance, then the electromagnetic performance is improved, but the risk of collision between rotor and stator increases due to manufacturing tolerances, temperature differences, and eccentricity
Solution Approach 1:
The control system performs preliminary measurements of airgap width at multiple positions around the circumference during operation, before collision can occur. Based on these measurements, the system proactively adjusts the magnetic force distribution to prevent airgap narrowing that would lead to collision, rather than reacting after the problem manifests
Solution Approach 2:
The system changes the magnetic force distribution parameters by injecting additional current into selected windings. This creates a localized additional magnetic force that compensates for eccentricity and prevents airgap narrowing in critical regions, allowing the machine to maintain a narrower overall airgap for better electromagnetic performance while ensuring reliability
2Reliability
If the airgap width is increased to avoid collision, then the reliability is improved, but the electromagnetic performance deteriorates
Solution Approach 1:
Instead of uniformly increasing the airgap width throughout the entire circumference, the system applies localized compensation by injecting current only into selected windings that correspond to regions with narrow airgaps due to eccentricity. This creates a locally enhanced magnetic force that maintains the airgap at critical positions without sacrificing overall electromagnetic performance
Solution Approach 2:
The system creates a compensating magnetic force field that effectively 'copies' or counteracts the detrimental effects of eccentricity. By generating an opposing magnetic force distribution, the system neutralizes the uneven airgap caused by manufacturing tolerances and operational conditions
3Reliability
If the electrical machine is down-regulated or shut down to avoid collision risk, then the reliability is improved, but the productivity and power output are reduced
Solution Approach 1:
The control system enables the electrical machine to self-correct airgap width issues by automatically injecting compensating current into selected windings based on real-time airgap measurements. This self-service capability eliminates the need for external intervention or shutdown, allowing continuous operation at full power output while maintaining reliability
Solution Approach 2:
The system implements a closed-loop feedback mechanism where airgap width is continuously measured at multiple positions, and the measurements are fed back to the control system. Based on this feedback, the control system dynamically adjusts the current injection to maintain optimal airgap width, enabling continuous full-power operation without collision risk
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 approach allows the electrical machine to operate continuously without risk of collision, maintaining high power output and efficiency by preemptively correcting airgap width issues, even under adverse conditions, and can be easily integrated into existing control systems.
Implementation Method 1
The width of the airgap is generally understood to be the shortest distance between magnets of the field and windings of the armature... the magnetic force over a narrower airgap region is greater than the magnetic force over a wider airgap region
Implementation Method 2
obtain a measurement of airgap width during operation of the machine
Implementation Method 3
temperature differences must be taken into account, since the armature generally reaches a higher temperature than the rotor on account of losses in the windings of the armature. Thermal expansion can decrease the height of the airgap
Data Source
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AI summary
The invention describes a method of controlling an electrical machine (2) comprising a rotor (20) and a stator (21) separated by an airgap (AG), which method comprises the steps of obtaining a measurement (wAG) of airgap width during operation of the machine (2); determining a corrective value of negative Id current (110) on the basis of the airgap width measurement (wAG); and injecting the negative Id current (110) into windings (210) of the electrical machine (2) to correct the airgap width. The invention further describes a control arrangement (1) of an electrical machine (2); and a wind turbine comprising a generator (2) and such a control arrangement (1).