Tests Completed on Advanced Generator for Wind Turbines

Significant cost cuts of wind turbine operation with brushless doubly-fed generators

The Challenge

Operating and maintenance costs have become a growing issue, particularly for off-shore wind farms. To overcome this, Control Techniques designed a brushless doubly-fed induction generator to make the wind turbine more reliable and also reduce the size requirement for the associated converter to one third of the generator rating.

The solution

The technology took 10 years to develop and a 20-kw machine was first tested in 2009. It was the world’s first brushless doubly-fed generator (known as a brushless dfig) fitted into a wind turbine. With sights set on a multi-mw machine, the team opted for intensive testing of a 250-kw brushless generator. Wind Technologies designed a test rig with 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,” explained 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 added.

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The Benefits

Wind technologies’ brushless dfig drastically cuts build costs (capex), as well as the level and frequency of maintenance (opex) required with the elimination of slip-rings and brush gear. The generator no longer requires brush carbon extraction equipment, further reducing manufacturing costs and no carbon brush dust spreads into the turbine nacelle due to brush wear. This also removes a major maintenance routine from the generator. These advantages become even more significant for off-shore wind turbines.

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

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