Autonomous renewable energy conversion system

This paper briefly reviews the need for renewable power generation and desc ribes a medium-power Autonomous Renewable Energy Conversion System (ARECS), integrating conversion of wind and solar energy sources. The objectives of the paper are to extract maximum power from the proposed wind energy conve rsion scheme and to transfer this power and the power derived by the photov oltaic system in a high efficiency way to a local isolated load. The wind e nergy conversion operates at variable shaft speed yielding an improved annu al energy production over constant speed systems. An induction generator OG ) has been used because of its reduced cost, robustness, absence of separat e DC source for excitation, easier dismounting and maintenance. The maximum energy transfer of the wind energy is assured by a simple and reliable con trol strategy adjusting the stator frequency of the IG so that the power dr awn is equal to the peak power production of the wind turbine at any wind s peed. The presented control strategy also provides an optimal efficiency op eration of the IG by applying a quadratic dependence between the IG termina l voltage and frequency V similar to f (2). For improving the total system efficiency, high efficiency converters have been designed and implemented. The modular principle of the proposed DC/DC conversion provides the possibi lity for modifying the system structure depending on different conditions. The configuration of the presented ARECS and the implementation of the prop osed control algorithm for optimal power transfer are fully discussed. The stability and dynamic performance as well as the different operation modes of the proposed control and the operation of the converters are illustrated and verified on an experimental prototype. (C) 1999 Elsevier Science Ltd. All rights reserved.