الفهرس 
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Abstract
Induction motors are the most widely used motors for appliances, industrial control, and automation. i.e. many electric loads are primarily induction motors. Hence they are often called the prime workhorse of the industry motion. They are robust, reliable, and durable. Motors consume more than 50 % of the total energy generated. For this reason it is important to optimize the efficiency of motor drive systems if significant energy savings are to be obtained. The induction motor (IM), especially the squirrel - cage type, is widely used in electrical drives and is responsible for most of the energy consumed by electric motors. The induction motor losses can be classified as follows: Stator copper losses. Rotor copper losses. Iron losses. Stray losses. Mechanical (friction + windage) losses. The main losses, are copper (stator + rotor) and iron losses. The focus of this research is to minimize these losses or maximizing the efficiency, that achieves a proper suitable deal of power factor improvement. The concept of energy saving has always been an attention grabber, especially when the promised savings are high and the potential for a reduction in running costs appears high. It is experienced that, the induction motor at fractional loads, is an inherently inefficient device, because its efficiency falls at light loads. So the aim here is to improve the efficiency especially at light loads. Some words should be putted into our consideration that, Only energy that is being wasted could be saved. In this research, it is hopeful to give a point of view on efficiency optimization problem and so the power factor improvement. By using sensorless speed control of I.M. Because controlled induction motor drives without mechanical speed sensors at the motor shaft have the attractions of low cost and high reliability. To replace the sensor, the information on the rotor speed is extracted from measured stator voltages and currents at the motor terminals. The artificial neural networks are used here to achieve goals of this research. This research demonstrates the procedure of obtaining the point of maximum efficiency and finding it depends only on the machine parameters. i.e. there is a unique point at certain slip or speed, and the voltage reduction used here to keep this speed of max. eff. with any load torque requirements. When operating at slip of max. eff. the motor characteristics are compared with the motor conventional ones operating at rated voltage. This to estimate the amount of energy saving achieved and the amount of power factor improvement. More over, it gives the suitable operating voltage such that the motor will run at its maximum efficiency at certain load torque. It presents also speed control by both voltage and frequency variations and keeping the magnetic saturation and insulation not to exceed their specified design values. After that, a view on the general - purpose voltage - frequency pattern is investigated to easily control the induction motor by frequency variation. It shows the effect of frequency variation on the motor performance characteristics. This study investigates the operation at optimum efficiency at variable frequencies.