Centrifugal controller of rotation frequency for vertical axis wind turbines

Abstract

The market for small vertical axis wind turbines (VAWTs) continues to grow rapidly, filling up especially the low wind potential locations. Since the Saudi Government has announced to install 9 GW of wind power by 2032, this ambitious plan could be at least partially improved by the small wind turbines, taking into account the low annual mean wind speed on the most Kingdom of Saudi Arabia territory.

However, the safety and durability of most commercially available VAWTs have not been adequately addressed with respect to the turbine over speed in high wind speed conditions.

The presented research gives a methodology for calculating a cost-effective dynamic braking controller, based on a centrifugal mechanical activation spring-load mechanism with a pendulum. The analysis is focused on a small two-tier 3 kW Darrieus VAWT, where a mechanically activated friction brake is deployed as the turbine rotational speed approaches a red line. The proposed method makes a small turbine absolutely safe on any available wind speed and/or during accidental electric load switch off. The analysis was made for a typically high continental wind speed of 25 m/s.

The paper presents the calculation model in VisSim software. Controller parameters were developed as the result of the research conducted on a functional turbine of the specific size in the model. The experiments covered two different cases: with a relatively low spring stiffness coefficient (400 N/m), showing the periodical oscillations of a controller pendulum on the cut-out speed and a high spring stiffness coefficient (4000 N/m), which the VAWT rotor can be surely braked at.

The paper is intended to provide the mathematical basis for the scientific analysis, as well as providing practical implementation information to engineers building similar turbines, including Savonius, Darrieus, H-Darrieus, helix shape, V-type, and any other types of rotating rotors. The estimated capacity utilization factor (CUF) of any VAWTs, when using the proposed centrifugal mechanical controller, can be increased twice to 82% for on-land small VAWTs.