A Generalized Approach to the Steady-State Efficiency Analysis of Torque-Adding Transmissions Used in Renewable Energy Systems

Abstract

The paper presents a general approach to the steady-state efficiency analysis of one degree of freedom (1-DOF) speed increasers with one or two inputs, and one or two outputs, applicable to wind, hydro and marine-current power generating systems. The mechanical power flow, and the efficiency of this type of complex speed increasers, are important issues in the design and development of new power-generating systems. It is revealed that speed increases, with in-parallel transmission of the mechanical power from the wind or water rotors to the electric generator, have better efficiency than serial transmissions, but their efficiency calculus is still a challenging problem, solved in the paper by applying the decomposition method of complex speed increasers into simpler component planetary gear sets. Therefore, kinematic, steady-state torque and efficiency equations are derived for a generic 1-DOF speed increasers with two inputs and two outputs, obtained by connecting in parallel two gear mechanisms. These equations allow any speed increaser to be analysed with two inputs and one output, with one input and two outputs, and with one input and one output. We discuss a novel design of a patent-pending planetary-gear speed increaser, equipped with a two-way clutch, which can operate (in combination with the pitch adjustment of the rotors blades) in four distinct configurations. It was found that the mechanical efficiency of this speed increaser in the steady-state regime is influenced by the interior kinematic ratios, the input-torque ratio and by the meshing efficiency of its individual gear pairs. The efficiency of counter-rotating dual-rotor systems was found to be the highest, followed by systems with counter-rotating electric generator, and both have higher efficiency than conventional systems with one rotor and one electric generator with fixed-stator.

A Comparative Performance Analysis of Counter-Rotating Dual-Rotor Wind Turbines with Speed-Adding Increasers

“…The in-parallel transmission of mechanical power from inputs to outputs can be achieved by power split at input, output or both, which ensures a higher efficiency compared to transmissions obtained by serial connection of the same component mechanisms [48]. A new approach to the development of modern wind turbines is the use of two counter-rotating coaxial rotors and the integration of a counter-rotating electric generator, which requires a mechanical transmission with power split at both input and output.…”

Dynamic Analysis of a Single-Rotor Wind Turbine with Counter-Rotating Electric Generator under Variable Wind Speed

“…A general approach to the steady-state efficiency analysis of speed increasers with both one or two inputs and one or two outputs is proposed in [31]. The authors concluded that the in-parallel or split-power transmissions used in wind turbines with either two counter-rotating rotors or a counter-rotating generator have higher efficiency than serial transmissions.…”

Comparative analysis of torque-adding wind energy conversion systems with a counter-rotating vs. conventional electric generator

“…Various innovative solutions of planetary speed increasers were proposed (Saulescu et al, 2016b;Saulescu et al, 2018;Neagoe et al, 2019) for counterrotating WECS. The performance in the steady-state regime of the different WECS configurations was investigated comparatively (Saulescu et al, 2016b;Neagoe et al, 2019;Saulescu et al, 2021;Neagoe and Saulescu, 2022), and a generalized approach for the efficiency analysis of 1-DOF speed increasers for counter-rotating WECS was proposed (Neagoe et al, 2020).…”

“…Recent research proved that the use of the counter-rotating generators can lead to a higher conversion efficiency of WECS than the conventional system (Saulescu et al, 2016a; Frontiers in Energy Research 02 frontiersin.org Saulescu et al 10.3389/fenrg.2023.1215509 2016b; Neagoe et al, 2017;Neagoe et al, 2019;Neagoe et al, 2020;Saulescu et al, 2021;Neagoe and Saulescu, 2022). However, only a few studies analyzed WECS configuration with both counterrotating rotors and counter-rotating generator and proposed suitable mechanical transmissions (Neagoe et al, 2019;Neagoe et al, 2020;Neagoe and Saulescu, 2022).…”

“…Recent research proved that the use of the counter-rotating generators can lead to a higher conversion efficiency of WECS than the conventional system (Saulescu et al, 2016a; Frontiers in Energy Research 02 frontiersin.org Saulescu et al 10.3389/fenrg.2023.1215509 2016b; Neagoe et al, 2017;Neagoe et al, 2019;Neagoe et al, 2020;Saulescu et al, 2021;Neagoe and Saulescu, 2022). However, only a few studies analyzed WECS configuration with both counterrotating rotors and counter-rotating generator and proposed suitable mechanical transmissions (Neagoe et al, 2019;Neagoe et al, 2020;Neagoe and Saulescu, 2022). To the best of our knowledge, a major research gap identified in the literature review was the need for comparative analysis of these types of WECS in different structural-functional scenarios that allow their constructive optimization and highlight their benefits in comparison with WECS with a conventional generator.…”