Hydrostatic Transmission to Improve Cost Efficiency and Power Reliability of Wind Power

Achievement date: 

Researchers at the NSF-funded Engineering Research Center (ERC) for Compact and Efficient Fluid Power (CCEFP), headquartered at the University of Minnesota, have developed hydrostatic transmissions (HST) that can replace mechanical gearboxes on utility-scale wind turbines. An industrial partner has agreed to test the solution in its offshore wind turbines to further evaluate potential benefits of HST on cost and power reliability.


High reliability and low maintenance are especially important in offshore wind turbines. Two of the highest maintenance costs in a wind turbine are for gearbox and generator bearing replacement, both which result from stresses incurred by the turbine system during high wind gusts. By replacing mechanical gearboxes with HST, such stresses can be reduced or eliminated. This reduces the need for power electronics on wind turbines, ultimately lowering cost, improving efficiency, and further improving power reliability.


In a utility-scale wind turbine, there is an 80–100 times increase in rotational speed between the turbine and the generator. This required speed increase is currently achieved with a mechanical gearbox. The gearbox experiences high loads during wind gusts and the resulting stresses are transferred from the gearbox to the generator, which will then require regular maintenance or replacement. Since the power path in CCEFP’s HST solution is hydraulic, the inherent compliance in the fluid provides a damping effect that results in a large stress reduction in the gearbox and generator during wind gusts. The HST, a continuously variable transmission, also allows the generator to run at constant speed regardless of wind conditions.