This paper presents a new control strategy of a stand-alone wind energy conversion system. The proposed system consists of a three pbase induction machine connected to a variable speed wind turbine through a step-up gear box. A current controlled voltage sonrce inverter (CC-VSI) with an electronic load controller (ELC) is connected in parallel with the main load to the AC terminaIs of the induction machine. The proposed control strategy is based on fuzzy logic control principles which enhance the system performance. There are three fuzzy logic PI controllers and one hysteresis cnrrent controller (HCC) which are used to extract the maximum available energy from the wind turbine as well as to regulate the generator terminal voltage simultaneously against wind speed and load variations. A complete mathematical model of the proposed system is developed in order to simulate its performance with the proposed control strategy. Simulation results using MatlabISimulink demonstrate the effectiveness of the proposed contrcl strategy in capturing the maximum available energy Grom the wind turbine and in regulation of the generated terminal voltage simultaneously against wind speed and load variations. d& ,-&I\ +I . &&I
There exists a combination of stator voltage and frequency which results in maximum efficiency for a given induction motor under a specified speed and load condition. This optimal operating point is calculated over the complete speed and load torque range using an Artificial Neural Network (ANN). It is shown that maximum efficiency can be achieved compared to the conventional volthertz control method. Theoretical results are presented as well as an experimental confirmation of them. Due to the wide application in process industries, the problem related to the efficiency maximization of induction motor has received much attention [I-21. Conventionally, the air-gap flux of a motor is maintained at a nominal value throughout the whole speed range, thus achieving a high utilization of the motor iron and permitting the development of the rated torque at all supply frequencies. However, at a light load, the motor flux is greater than necessary for the development of the required torque, and loss is high, resulting in poor motor efficiency. Its efficiency can be improved by reduction of the air-gap flux to a value suitable for the reduced torque. The effect of flux level on the efficiency of an induction motor can be understood from [3-61. The combination of stator voltage and frequency, which minimizes the induction motor losses, was shown to be complex fbnction of the operating
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