Variable Exciter Current Control for Synchronous Generator Air Gap
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Solution Overview
Problem
Large wind power installations with synchronous generators face challenges in reducing weight while maintaining efficiency, as the air gap thickness variations due to elasticities and asymmetries lead to increased material usage and costs, and existing technologies do not effectively manage these variations.
Innovation Solution
A method of controlling exciter currents in a synchronous generator to adjust for varying air gap thicknesses by differentiating the current flow through pole windings based on position, elasticity, and magnetic field measurements, allowing for individual control of exciter currents to maintain optimal magnetic flux and reduce material requirements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the air gap thickness is reduced to decrease magnetic reluctance and increase magnetic flux density, then the radial force density increases and can cause contact between pole wheel and stator, but increasing mechanical stiffening to avoid contact greatly increases material usage and generator mass
Solution Approach 1:
The patent applies dynamics by making the exciter currents variable rather than constant. The control device adjusts the exciter currents dynamically based on measured air gap thicknesses, allowing the magnetic field strength to adapt to local conditions. This dynamic adjustment enables the system to maintain reliable magnetic flux density without requiring excessive mechanical stiffening, thereby reducing generator mass.
Solution Approach 2:
The patent changes the parameter of exciter current from a uniform constant value to variable values based on position. By measuring air gap thickness at different locations and adjusting exciter currents accordingly, the system optimizes magnetic flux density locally. This parameter change allows reduced mechanical stiffening requirements, leading to lower material usage and generator mass while maintaining reliability.
2Device complexity
If uniform exciter currents are used through all pole windings, then the control system is simple, but variations in air gap thickness due to elasticities and asymmetries cannot be compensated, leading to suboptimal magnetic flux distribution
Solution Approach 1:
The patent applies local quality by assigning different exciter currents to different pole windings based on their local air gap conditions. Instead of uniform current distribution, each pole winding receives a tailored exciter current determined by its specific air gap thickness. This localized control optimizes magnetic flux distribution across the generator, improving reliability while the added complexity is managed through automated measurement and control.
Solution Approach 2:
The patent implements feedback by measuring air gap thicknesses at various locations and using these measurements to adjust exciter currents. The control device continuously monitors air gap variations and modifies exciter currents accordingly, creating a closed-loop system. This feedback mechanism compensates for elasticities and asymmetries, ensuring optimal magnetic flux distribution without excessive system complexity.
3Strength
If mechanical stiffening is increased to absorb magnetic forces and prevent contact, then reliability is improved, but material usage and manufacturing costs increase significantly
Solution Approach 1:
The patent replaces mechanical stiffening with an electromagnetic control solution. Instead of relying solely on mechanical structures to absorb magnetic forces and prevent contact, the system uses variable exciter currents to actively manage magnetic flux distribution. This substitution reduces the need for excessive mechanical stiffening, thereby reducing material usage and manufacturing costs while maintaining or improving reliability through active control.
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 reduces the weight of the generator by optimizing air gap thickness and magnetic flux, thereby enhancing the weight-to-power ratio and minimizing material usage without compromising performance.
Implementation Method 1
The aerodynamic rotor is caused to rotate by wind and thereby drives an electromechanical rotor of a generator. In that respect the present invention concerns a wind power installation which uses a synchronous generator. Thus a pole wheel or motor rotor of the synchronous generator is rotated relative to a stator of the latter. Electric current is generated in the stator by the relative rotary movement of the pole wheel with respect to the stator so that kinetic energy of the wind is converted into electric energy.
Implementation Method 2
A respective exciter current is controlled through each pole winding. At least one of the exciter currents is varied relative to at least a further one of the exciter currents. Between the pole wheel and the stator there is an air gap which represents a considerable magnetic reluctance in a magnetic circuit between pole wheel and stator.
Implementation Method 3
Between the pole wheel and the stator there is an air gap which represents a considerable magnetic reluctance in a magnetic circuit between pole wheel and stator. That magnetic reluctance depends in particular on the thickness of the air gap and the thickness of the air gap is therefore selected to be as small as possible.
Implementation Method 4
Elasticities of the components and thus as a result in particular the pole wheel and possibly also the stator can also lead to differing thicknesses of the air gap in the peripheral direction, more specifically in particular under the influence of mass, gravitational and magnetic forces.
Implementation Method 5
Elasticities of the components and thus as a result in particular the pole wheel and possibly also the stator can also lead to differing thicknesses of the air gap in the peripheral direction, more specifically in particular under the influence of mass, gravitational and magnetic forces.
Data Source
AI summary
The present invention concerns a method of controlling a wind power installation having a generator with a stator, a pole wheel with at least two rotor poles with a respective pole winding for producing a magnetic field guided in the respective rotor pole, and an air gap between the stator and the pole wheel, including the steps—controlling a respective exciter current through each pole winding,—varying at least one of the exciter currents relative to at least one further one of the exciter currents, and/or—varying at least one of the exciter currents in dependence on the position of the pole wheel in relation to the stator.