Manufacturing tolerances influence permanent magnet synchronous generator generator (PMSG) performance

Introduction

The SWIP project (‘New innovative solutions, components and tools for the integration of wind energy in urban and peri-urban areas’) aims to expand the market for Small Wind Turbines in Europe by developing, implementing and testing innovative solutions and components. Developments carried out through SWIP project will allow to improve performance, reduce maintenance costs, and encourage integration of turbines into urban and peri-urban areas by a holistic approach.
Within this project, permanent magnet generator and converter system has been designed and manufactured in order to reach a high efficiency system. Both components, generator and converter, are designed considering the different features of the pilot site:
• Noise level limits stablished for the local regulation (urban area, educational area,..)
• Weight and size generator limits
• Wind resource in the pilot site
• Converter connection type: Connected to the grid or in island operation
Furthermore, another technical aspects like Cp-λ curve of the blades or converter limits, such us maximum voltage or modulation level, are considered during the design stage.
Taking to account all these aspects, a permanent magnet synchronous generator (PMSG) has been designed. PMSG are selected due to advantages like high power density, high efficiency, simplification in the construction, low losses and free maintenance. One of the disadvantages of this technology is the permanent magnet price and the deterioration of magnetic properties with the temperature.
From design stage, performed by simulation, to manufacturing stage several considerations must be taking into account to avoid that the real system behavior differs from the expected. One of them is the manufacturing tolerance, which can affect the machine behavior. Electrical parameters such as system efficiency or no-load voltage values could be influenced by the differences between real and theoretical dimensions. Therefore, manufacturing tolerances must be considered during the design stage.


Approach

In order to evaluate the manufacturing tolerances effects in designed PMSG behavior, several studies are performed. PMSG is modelled in FLUX 2D, a finite element software used for electromagnetic application. From these studies, electrical parameters such as no-load voltage, electric power and cogging torque will be evaluated and corrective actions may be taken into account before the manufacturing stage.

Main body of abstract

Within SWIP project, a PMSG based wind turbine has been designed and manufactured to be installed in an educational area.
During the design stage, several finite element studies has been performed to evaluate the PMSG behavior, including no-load voltage, generated power, or cogging torque analysis among others. During this stage no machine deformations are considered, that is, the rotor is perfectly cylindrical and the gap is uniform. When the real prototype is manufactured, these assumptions may not be valid, due to dimensional tolerances. Therefore, before PMSG manufacturing stage, a previous analysis must be done considering the influence of eccentricity and rotor deformation, which make a non-uniform gap.
This study allows to identify possible differences between the PMSG behavior expected from simulation studies and measurements obtained in the test bench and later when the generator is installed in the wind turbine.


Conclusion

In this paper, it is shown the aspects that must be considered to design a high efficiency PMSG. The influence of dimensional tolerances in PMSG behavior is evaluated before its manufacturing. In particular, the influence of eccentricity and rotor deformation in electrical parameters such as no-load voltage, electric power and cogging torque are evaluated by finite element simulations.
The evaluation of this influence will allow to predict deviations of the real system from theoretical PMSG behavior, and make the necessary corrective actions on the design if needed.



Learning objectives
To evaluate the dimensional tolerances influence on the real PMSG behavior in order to predict deviation on electrical parameters before the manufacturing.