Probabilistic Analysis of Continuously Variable Transmission to Increase Reliability

Abstract

Renewable energy has surfaced as a power source of interest of the world recently. Wind Energy has been the leading source of renewable energy development for the past several years. The biggest issue with wind energy are wind turbine (WT) drivetrain failures. The gearbox fails after three to seven years of operation while the expected lifetime of the WT is 20 years. The application to the automotive industry inspired the use of continuously variable transmissions (CVT) in a WT. The CVT considered in this study is the Nu-Vinci CVT technology, a Continuously Variable Planetary (CVP) transmission, designed by Fallbrook Technologies. This technology was selected because of its planetary configuration and its ability to transmit larger amounts of torque, which is required for WT applications. The goal of this research was to reduce the Cost of Energy (COE) by increasing the reliability of CVTs in WTs. In this study, two WT systems, one with CVT as the third stage (referred as ‘WT with CVT’) and another with three stage standard gearbox (referred as ‘WT with SG’), are considered. The research question in this study is ‘Does the use of CVTs improve the reliability of drivetrains of WTs?’ To answer this question three specific aims were developed. First, a computational framework had to be developed. Second, a probabilistic dynamic analysis was conducted. Third, a probabilistic analysis on the COE was performed. A computational framework was developed to guide the probabilistic analysis to determine power values and COE. The probability that the generator torque of the WT with CVT will be less than that of the WT with SG is found to be 50.67%. It was also shown that provided the same input speed and torque, the WT with CVT has a slightly higher power generation. In addition, it was shown that there is 54% probability that the WT with CVT will exhibit lower COE than WT with SG. The higher power production is attained while decreasing the COE. From these results, it can be inferred that the reliability of the drivetrain is improved using a CVT.