Pergamon Solar EnergyVol.61, No. 2. pp. 119.-125, 1997 0 1997 Elsevier Science Ltd PII: SOO38492X (Iy7)00034-0 All rights reserved.Printed in Great Britain 0038-092x/93 $17oo+o.oo ELECTROMECHANICAL CONVERTERS ASSOCIATED TO WIND TURBINES AND THEIR CONTROL MAXIME SADRE+ Laboratoire d’Informatique AppliquCe, Tour 55. Couloir 55-65, 1” &age, Porte 8, LJniversitCPierre et Marie Curie, 4 Place Jussieu, 75252 Paris, Cedex 05, France Received 10 May 1996; revised version accepted 17 February 1997 Communicated by DAVID MILBORROW Abstract-In this paper is presented a classification of converters liable to be associated to wind turbines. A detailed classification of electromechanical converters has been given. Different methods of control of these converters have been discussed; among which the maximum power point tracking method is of particular interest. It responds well to various criteria such as precision, stability, rapidity and auto- adaptability. Q 1997 Elsevier Science Ltd. 1. INTRODUCTION 3. CONTROL OF WIND TURBINES Optimal conversion of wind energy necessitates a judicious choice of wind turbine, converter and control device. The converter is chosen to satisfy the utilization conditions and match best the load. Generally the complexity of the con- trol device will depend on the power range of the wind turbine. 3. I. Control of revolution speed In some applications it is necessary to main- tain constant or nearly constant revolution speed, e.g. an induction three-phase generator connected to a grid should operate at approxi- mately constant speed. Generally, this is obtained by means of a mechanical controller acting on pitch angle. 2. CONVERSION OF WIND ENERGY 2. I. Clussification of converters Two types of wind energy converters can be distinguished: ( 1) homogenous: mechanical converter - centrifugal pump, piston pump; (2) heterogeneous: ( 1) electromechanical converter - generator; (2) mechanical-thermal converter: heating by Eddy currents, heat pump. Storage of the energy converted permits to remedy the random nature of wind energy. Table 1 gives a classification of converters liable to be associated to wind turbines. It should be noted that the tables presented in this paper are not exhaustive. A classification of electrome- chanical converters liable to be coupled to wind turbines is established in Table 2 (Fitzgerald et al., 1971). ‘Present address: 24 Rue M. Berthelot, 92120 Montrouge, France. 3.1. Control of power The optimal available power of a wind tur- bine is a cubic function of wind speed k,03 (or the revolution speed P=k,n3). If the receptor possesses a characteristic governed by the rela- tionship P=k3n3, where k3 tends towards k,, the power adaptation would be intrinsically obtained. Therefore, in the design of such a receptor one should endeavour that its charac- teristic coincides with that of the wind turbine used (Fig. 1). The attempts undertaken on direct adaptation have been conclusive only for some mechanical-thermal converters and pumps; consequently the use of a controller is indispensable in most cases. The power optimi- zation may be performed on either wind turbine mechanical power or converter output power. In the latter case, the efficiency of all the con- version system elements will affect the overall efficiency of the system. 3.3. Use of adapters It is often necessary to insert a static converter (adapter) in the conversion system in order to adapt the receptor to the electromechanical 119