Eliminating the gearbox is a priority for turbine makers because the direct-drive approach improves reliability, reduces operating and maintenance costs, and improves annual energy output— all of which helps to reduce the cost per kilowatt (kW) hour—a critical element for increasing turbine sales. The challenge to launching a gearless turbine is that today’s direct-drive generator systems for MW wind applications are all too large in diameter to fit inside an existing nacelle. Until now, launching a direct-drive turbine required a complete redesign which takes four to six years and tens of millions in capital investment.

Exro’s VIEG completely changes the launch cycle for turbine manufacturers because our unique geometry makes it possible to replace the legacy gearbox and induction generator with a new direct-drive permanent magnet machine of the same size and weight. The benefit of this “plug and play” approach is that it greatly reduces the cost and time required for a turbine manufacturer to gain competitive advantage by launching a new premium direct-drive version of a legacy turbine model.

“Plug and play” is not the only advantage that the VIEG delivers. Our patented rotating electromagnetic machine is paired with a proprietary control and switching system which enables the machine to be reconfigured in real-time—matching changes in the energy source. This self-optimization capability provides a significant increase in energy output, and it also helps reduce downstream losses in the power electronics by optimizing the output signal to keep it within a tightly controlled band of variability.

Electrical generators are very efficient when the energy source spins their shafts at a pre-specified speed and torque, but their efficiency drops precipitously when the energy source varies up and down. To compensate for variability, engineers place sophisticated machinery between the energy source and the generator in an attempt to buffer these swings, so that the generator operates as if the energy source is stable. Historically, the reliance has been on pitch and yaw systems combined with massive gearboxes, but these are expensive and prone to breakdown. More recently, engineers have begun to link multiple generators together, typically with mechanical gearboxes, so that individual generators can be added (or taken away) in an attempt to match the generator capacity with the available energy as it swings up and down. This approach is complex and involves even more gearbox issues, but the gains in output have been greater than the cost, so efforts continue in this direction.

Exro’s solution follows a similar logic to a multi-generator approach, but the VIEG takes the concept to a much higher level by completely redesigning the electrical generator for variable input sources. Rather than connecting a string of individual legacy machines together through mechanical gearing, the VIEG is a single machine made up of a series of paired coils combined with an intelligent controller and high-speed electronic switching. The coils are configured in magnetically “balanced stages”, which allows the use of permanent magnets while simultaneously reducing cogging torque to a bare minimum. This unique geometry allows the VIEG to operate efficiently at extremely low wind speeds. As available energy increases, the VIEG matches generator resistance to source energy by electronically adding generator stages. Conversely, the VIEG is able to drop stages as available energy (in this example wind speed) drops, cycling up and down without hesitation and without unnecessary mechanical friction. The need for a gearbox is eliminated, and a single VIEG generator scales up and down with available energy in a way that would take almost 70 traditional generators to match. The result is a self-adapting system with a lower cost and weight and a broader operational range than traditional machines.

The benefits of the VIEG are highly compelling: reduced capital cost, reduced weight, reduced mechanical energy loss, reduced power electronics losses, enhanced fault tolerance, less carbon output, and a substantially higher economic output. In order to reduce our reliance on coal, higher economic output is critical, a benefit the VIEG delivers in spades. Current modeling estimates show double digit gains in economic output (depending on configuration) after installing a VIEG rather than a traditional generator in a typical MW class wind turbine.

For a turbine maker, upgrading a legacy turbine (gearbox and induction generator) to the VIEG direct-drive power conversion train is the fastest and lowest risk path to launching a next generation direct-drive turbine model. The enhanced value proposition to their customer is simple… buy our direct-drive turbine and receive a higher ROI through increased annual energy production combined with lower O&M costs. Those turbine makers who launch direct-drive ahead of their competition will benefit from the opportunity to increase both market share and margin.