A Novel Digitalized Hydrostatic Drive Solution for Modern Wind Turbine

Abstract

Gearbox is a concern in modern wind turbines, increasing the maintenance cost and therefore the cost of energy (COE). A hydrostatic transmission (HST) improves the turbine drivetrain reliability by using slightly compressible mineral oil as the working medium rather than a rigid gearbox. An HST eliminates the power converter since it is a continuous variable transmission (CVT), making the turbine simpler and more cost effective. The turbine operates below the rated wind speed for a considerable time in a year, making the variable hydraulic motor run at partial displacement for the most common configuration of a hydrostatic wind turbine, a fixed displacement pump and a variable displacement motor. This results in low drivetrain efficiency. Moreover, large variable displacement motors for megawatt turbine are commercially unavailable. A digitalized hydrostatic drive for a modern wind turbine is proposed to improve the drivetrain efficiency at low wind speeds. The digital coding method for hydrostatic wind turbine is studied. A dynamic simulation model of the digitalized hydrostatic (dHST) wind turbine has been developed in Simulink. A widely used efficiency model for the hydrostatic pump and motors is used in the simulation to make the study practical. The proposed digitalized hydrostatic solution has been compared with a conventional hydrostatic solution. Simulation results show the benefits of digitalized hydrostatic transmission over conventional hydrostatic transmission in drivetrain efficiency, system complexity and cost.