AIMS Energy, 2020, 8(2): 156-168. doi: 10.3934/energy.2020.2.156

Research article

Export file:


  • RIS(for EndNote,Reference Manager,ProCite)
  • BibTex
  • Text


  • Citation Only
  • Citation and Abstract

Making a case for a Non-standard frequency axial-flux permanent-magnet generator in an ultra-low speed direct-drive hydrokinetic turbine system

1 Department of Mechanical Engineering, Faculty of Engineering, Khon Kaen University, Khon Kaen 40002, Thailand
2 Faculty of Engineering, Nakhon Phanom University, Nakhon Phanom 48000, Thailand
3 Department of Electrical Engineering, Faculty of Engineering, Khon Kaen University, Khon Kaen 40002, Thailand

This research project investigates the impacts of the rotor and generator sizes on rotational speed and voltage output of a direct-drive hydrokinetic turbine system. It searches for a possibility of reducing the generator size while possessing the capability to produce sufficient voltage at an ultra-low RPM. The system has a Darrieus rotor that directly drives an axial-flux permanent-magnet generator, hence the friction loss from the transmission system is eliminated. However, the direct-drive system possesses a very low rotational speed, which adversely affects the generator. In particular, the output voltage is not sufficient for regular applications or the generator diameter needs to be enlarged. Numerical models of the rotor and generator were constructed in MATLAB. The rotor and generator sizes were varied under several design conditions. The models delivered design parameters for the system and their relationships. It was found that designing the generator with 50/60 Hz electrical frequency limits the number of slot/phase and hence the maximum output voltage. The study makes a case for designing a generator with electrical frequency other than the standard frequency, where it would be novel to be able to produce a higher voltage when a location with high water velocity is available, in addition to an improved power production. It would allow the generator to produce higher voltage at a given water velocity and rotational speed or have a smaller diameter at a given output voltage.
  Article Metrics


1. Anyi M, Kirke B (2011) Hydrokinetic turbine blades: Design and local construction techniques for remote communities. Energy Sustainable Dev 15: 223-230.    

2. Davila-Vilchis JM, Mishra RS (2014) Performance of a hydrokinetic energy system using an axial-flux permanent magnet generator. Energy 65: 631-638.    

3. Alden Research Laboratory, How to evaluate hydrokinetic turbine performance and loads. Alden Research Laboratory, (n.d.). Available from:

4. Bravo R, Tullis S, Ziada S (2007) Performance testing of a small vertical-axis wind turbine.

5. Khalid SS, Liang Z, Qi-hu S, et al. (2013) Difference between fixed and variable pitch vertical axis tidal turbine-using CFD analysis in CFX. Res J Appl Sci Eng Technol 5: 319-325.

6. Ferreira AP, Silva AM, Costa AF (2007) Prototype of an axial flux permanent magnet generator for wind energy systems applications. 2007 European Conference on Power Electronics and Applications, Aalborg, Denmark.

7. Bannon N, Davis J, Clement E (2013) Axial flux permanent magnet generator, University of Washington, Seattle, WA, USA.

8. Khalid SS, Zhang L, Shah N (2012) Harnessing tidal energy using vertical axis tidal turbine. Res J Appl Sci Eng Technol 5: 239-252.

9. Behrouzi F, Maimun A, Nakisa M, et al. (2014) An innovative vertical axis current turbine design for low current speed. J Technol 66: 177-182.

10. Yassin A, Shahidul MI, Syed Shazali ST, et al. (2013) Optimization of green energy extraction: an application of cross-flow micro-hydro turbine. 6th International Engineering Conference (ENCON 2013), Kuching, Sarawak, Malaysia.

11. Zero Emission Resource Organization, Small-scale water current turbines for river applications. Zero Emission Resource Organization, (2010). Available from:

12. Urbina R, Peterson ML, Kimball RW, et al. (2013) Modeling and validation of a cross flow turbine using free vortex model and a modified dynamic stall model. Renewable Energy 50: 662-669.    

13. Deglaire P, Eriksson S, Kjellin J, et al. (2007) Experimental results from a 12 kW vertical axis wind turbine with a direct driven PM synchronous generator. Proc EWEC 2007-European Wind Energy Conference & Exhibition, Milan, Italy.

14. Eriksson S (2008) Direct driven generators for vertical axis wind turbines, Acta Universitatis Upsaliensis, Uppsala, Sweden.

15. Eriksson S, Bernhoff H, Leijon M (2011) A 225 kW direct driven PM generator adapted to a vertical axis wind turbine. Adv Power Electron 2011: 1-7.

16. Rovio T, Vihriaelae H, Soderlund L, et al. (2001) Axial and radial flux generators in small-scale wind power production, Tampere University of Technology, Tampere, Finland.

17. Zhao G, Yang RS, Liu Y, et al. (2013) Hydrodynamic performance of a vertical-axis tidal-current turbine with different preset angles of attack. J Hydrodyn 25: 280-287.    

18. Lanzafame R, Mauro S, Messina M (2014) 2D CFD modeling of H-Darrieus wind turbines using a transition turbulence model. Energy Procedia 45: 131-140.    

19. Çetin NS, Yurdusev MA, Ata R, et al. (2005) Assessment of optimum tip speed ratio of wind turbines. Math Comput Appl 10: 147-154.

20. Hall TJ (2012) Numerical simulation of a cross flow marine hydrokinetic turbine, University of Washington, Seattle, WA, USA.

21. Sheldahl RE, Klimas PC (1981) Aerodynamic Characteristics of seven symmetrical airfoil sections through 180-degree angle of attack for use in aerodynamic analysis of vertical axis wind turbines, Sandia National Laboratories, Albuquerque, NM, USA.

22. Gieras JF, Wang RJ, Kamper MJ (2008) Axial Flux Permanent Magnet Brushless Machines, 2 Eds., Springer.

© 2020 the Author(s), licensee AIMS Press. This is an open access article distributed under the terms of the Creative Commons Attribution Licese (

Download full text in PDF

Export Citation

Article outline

Show full outline
Copyright © AIMS Press All Rights Reserved