On the Accuracy of a Stewart Platform: Modelling and Experimental Validation

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Conceptual Synthesis of Speed Increasers for Wind Turbine Conversion Systems

Most wind turbines (WT) are of the single-rotor type, which means they are simple, reliable and durable, but unlikely to convert more than 40% of the available wind energy. Different solutions are proposed to minimize WT energy loss and improve performance, such as the use of speed increasers, counter-rotating wind rotors or counter-rotating electric generators. Downsizing the design, saving weight and reducing the cost of WT conversion systems, while increasing their efficiency, have posed constant challenges to WT designers. Nevertheless, very little research in the field is concerned with, and partially recommends, the design of conversion systems. Therefore, the aim of this paper is to propose a specific algorithm for the conceptual synthesis of speed increasers integrated in WT conversion systems, starting with an inventory of all combinations of the main components of a conversion system that prove compatible for efficient functioning. The algorithm is structured in two sections: the first one includes a four-step approach to WT system design, while the second one follows a three-step procedure for identifying the speed increaser concept. Twenty-two variants of speed increasers are further generated and analyzed, four of which are innovative solutions proposed by the authors. The paper also provides guidelines for identifying the WT conversion system concept according to the circumstances of its application

A generalized approach to the efficiency analysis of torque-adding transmissions used in renewable energy systems

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

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 Four Wind Turbines with Counter-Rotating Electric Generators

Wind energy conversion systems play a major role in the transition to carbon-neutral power systems, and obviously, a special attention is paid in identifying the most effective solutions for a higher valorization of the local wind potential. In this context, this paper presents a comparative study on the energy performances of wind turbines (WTs) that include a counter-rotating electric generator. Starting from an innovative concept proposed by the authors for a reconfigurable wind turbine with three clutches, four cases of WTs with counter-rotating generators are studied: a system with three wind rotors (WRs) and a 2-DOF (degrees of freedom) planetary speed increaser (Case A), with two counter-rotating WRs and a 1-DOF (Case B) or a 2-DOF (Case C) speed increaser and a 1-DOF single rotor wind system (Case D). An analytical archetype model for angular speeds, torques, powers and efficiency of the reconfigurable planetary speed increaser, corresponding to the general case with three inputs (Case A), was firstly derived. The analytical models of the other three cases (B, C and D) were results by customizations of the archetype model according to the kinematic- and static-specific effects of engaging/disengaging the clutches. The simulation of the analytical models for a numerical representative example with two variable parameters (input speed ratio kω and input torque ratio kt) allows highlighting the influence of various parameters (number of WRs, speed increaser DOF, kω and kt) on the input powers, power that flows through the planetary transmission and mechanical power supplied to the electric generator, as well as on the transmission efficiency. The obtained results show that the output power increases with the increase of the number of wind rotors, the transmission efficiency is the maximum for kt=1 and the speed amplification ratio increases with the ratio kω

A Comparative Performance Analysis of Four Wind Turbines with Counter-Rotating Electric Generators

Wind energy conversion systems play a major role in the transition to carbon-neutral power systems, and obviously, a special attention is paid in identifying the most effective solutions for a higher valorization of the local wind potential. In this context, this paper presents a comparative study on the energy performances of wind turbines (WTs) that include a counter-rotating electric generator. Starting from an innovative concept proposed by the authors for a reconfigurable wind turbine with three clutches, four cases of WTs with counter-rotating generators are studied: a system with three wind rotors (WRs) and a 2-DOF (degrees of freedom) planetary speed increaser (Case A), with two counter-rotating WRs and a 1-DOF (Case B) or a 2-DOF (Case C) speed increaser and a 1-DOF single rotor wind system (Case D). An analytical archetype model for angular speeds, torques, powers and efficiency of the reconfigurable planetary speed increaser, corresponding to the general case with three inputs (Case A), was firstly derived. The analytical models of the other three cases (B, C and D) were results by customizations of the archetype model according to the kinematic- and static-specific effects of engaging/disengaging the clutches. The simulation of the analytical models for a numerical representative example with two variable parameters (input speed ratio kω and input torque ratio kt) allows highlighting the influence of various parameters (number of WRs, speed increaser DOF, kω and kt) on the input powers, power that flows through the planetary transmission and mechanical power supplied to the electric generator, as well as on the transmission efficiency. The obtained results show that the output power increases with the increase of the number of wind rotors, the transmission efficiency is the maximum for kt=1 and the speed amplification ratio increases with the ratio kω