RFL’s Unique Design is Proving Extremely Valuable

By the end of 2015, 23.7% of energy was delivered from renewable sources with 3.7% of the total worldwide electricity supplied by wind energy, which is growing at a rapid rate of 17% per annum.

Since 2011, the cost of wind generating infrastructure has fallen by 10%, making wind energy 14% cheaper than new coal and 18% cheaper than new gas.

There are a variety of electrical generators on the market for use in micro-wind turbine applications. These include induction and synchronous machines.

High-end machines use permanent magnet generators – they’re excellent because they eliminate the copper losses associated with rotor windings, making them far more


efficient than induction and wound rotor machines. As such, these generators have gained interest in replacing conventional machines with Permanent Magnet Synchronous Generators (PMSG).

Until recently, wind energy converters have been designed for speeds from 750RPM up to 1800RPM, whereas wind turbines usually operate from 20RPM to 250RPM [3]. Consequently, a gearbox has been the link between the wind turbine and the generator. Gearboxes require maintenance, decrease efficiency, are noisy and are generally the first component to fail in the system.

By increasing the number of poles in the generator, the electrical frequency increases and the gearbox can be eliminated. PMSG are able to have a smaller pole pitch and therefore more poles as only the leakage flux between the two magnets sets the limitation.

Radial Flux Laboratories (RFL) has experience in modelling and developing machines utilising concentrated fractional windings which does not require an integer slot winding and hence allows for a higher pole count.

There are advantages with both an inner and outer rotor configuration which is generally designed around the application. An inner rotor (meaning the stator is on the outside) is the most typical design and is generally chosen as the majority of losses are contributed to by the copper losses within the stator. As a result, designing with the stator on the outside gives better cooling properties for a higher efficiency. Furthermore, having the stator on the outside allows for larger slots, and consequently a more efficient or higher rated machine.

A unique outer rotor design does bring a number of advantages though. For example, the larger rotor diameter allows for a higher number of poles, and the magnets stay cooler so the likelihood of demagnetisation is reduced. Additionally, the hub allows for the blades to be directly fixed to the rotor which results in a cheaper, simpler, and more integrated design.

Dual stator machines are now being considered for various motor and generator applications. The dual stator is incorporated in synchronous generators to increase the power capability.

Recently dual stators have been found to be useful as a part of uninterruptable power supplies, standalone power supplies, and generators of both ac and dc electric power [4]. Another advantage is the reliability of having a dual winding generator.

However, dual winding machines have also traditionally had the challenge of required heat dissipation associated with the inner winding. Recognising this, RFL has developed a unique design which transfers heat from both the inner and outer stator to the casing and cooling fins.

RFL has also optimised the mechanical structure, efficiency and thermal properties. This design shows promise in wind turbine applications, where the generator is required to be sealed for increased reliability and service timeframes.

As wind energy continues to grow it is paramount that wind turbines/generators are optimised for maximum efficiency and reliability. RFL has developed the most efficient and reliable generators on the market with the smallest footprint that can be tailored to meet the wind turbines design.


[1] Renewable Energy World. (2013). 100 Percent Renewable Vision Building [Online]. Available FTP: http://www.renewableenergyworld.com/articles/2013/04/100-percent-renewable-vision-building.html?amp%253bbuffer_share=fdc06

[2] C.Techies, “Renewables now cheaper than fossil fuels in Australia,” Environmental and Energy Study Institute, pp.1, Jan. 2013.

[3] M.Widyan, “Design, optimization, construction and test of rare-earth permanent magnet electrical machines with new topology for wind energy applications” in Phd Thesis. Berlin: Technical University of Berlin, 2006, pp. 16-76

[4] A.Dwivedi and R.K.Srivastava, “Analyses of Dual Stator PM Brushless DC Motor” in IOSR Journal of Electrical and Electronics Engineering (IOSRJEEE), Volume 1, Issue 2, pp 51-57


Credit: Ezra Bowen

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