Novel Speed Increaser Used in Counter-Rotating Wind Turbines

Abstract

The speed increasers are typical components of a large diversity of renewable energy systems (RES), like wind turbines or hydropower plants, used to harmonize the low input speed of wind rotor/hydro turbine with the higher speed requirement of the electric generator. The counter-rotating turbines are able to generate more electricity in comparison with the classical systems with one input due to the summation of the two independent input speeds and implicitly of two power flows, but they have a relatively complex control for matching the generator requirements. This drawback can be mitigated by using 1 degree of freedom (DOF) speed increasers with more inputs and one output. The paper deals with the kinematic and static analysis of a novel 1DOF planetary transmission, with two inputs and one output, used as speed increaser in wind/hydro RES. Starting from its property of summing two external torques and the speed amplification ratio imposed on the main power flow, the transmitting functions of speeds and torques, considering gear friction, as well as the mechanism efficiency are established in the paper. A dimensionless parameter k, defined as ratio of the input torques, is introduced and, based on numerical simulations, the transmission behaviour is highlighted. The results allow the formulation of useful recommendations for optimal design of planetary transmissions implemented in RES.