Advanced generator passes wind turbine tests 13 April 2012

Wind Technologies reports that it has completed testing on a radical generator design – one that could seriously cut the cost of both operations and maintenance for wind turbines.

Its design is essentially a brushless doubly-fed induction generator, claimed not only to increase the reliability of wind turbines, but also to reduce the size for the associated converter – to one-third of the generator rating.

The firm's technology was developed at Cambridge and Durham Universities and a 20kW prototype was tested in a Gazelle wind turbine in 2009 – the world's first brushless doubly-fed generator (known as a Brushless DFIG) on a wind turbine.

This proved the theoretical models, but to move up to a multi-MW machine, the team needed to test a 250kW brushless generator, built to its specifications by ATB Laurence Scott in Norwich.

The test rig has a double power feed – mains power and connection via the controlling inverter drive – with a Control Techniques Unidrive providing grid connection.

"We chose Control Techniques partly because it is a British product, but mainly because of the excellent support," explains Dr Paul Malliband, vice president of engineering at Wind Technologies.

"It's always possible to get hold of an engineer to help with a technical query, even during weekends. We have developed a very good relationship over the period of this project," he says.

Wind Technologies' Brushless DFIG has two stator windings of different pole numbers in a single frame, chosen so that there is no direct coupling, in combination with a special form of rotor that can couple both fields.

Malliband claims serious capex and opex cost reductions, because the generator no longer requires brush carbon extraction equipment and no carbon brush dust spreads into the turbine nacelle, due to wear.

Because the Brushless DFIG has doubly-fed operation, it only requires a fractionally rated converter, again saving overall costs, he explains. It also shows greater compatibility with grid codes than the conventional DFIG, thereby providing further capex benefits.

Brian Tinham

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