الفهرس 
الملخص العربى
GeneralOnly 14 pages are availabe for public view
 |  | from | 252 |  |  |
| | | from | 252 | | |
Abstract
In many applications such as: tracking drives, lifting tools, low speed and high torque are needed. As the developed electromagnetic torque of the 3-phase induction motor increases with the decreasing of the power supply frequency, the frequency division is used to increase the motor torque. And consequently the motor speed will decrease. To realise such grequency division, a certain technique is used. This technique depends on eliminating some half cycles of the power supply line current wave form. The resulting wave form has a divided frequency. The frequency division technique can be achieved by using a voltage controller contains a set of six thyristors. Two anti parallel thyristors for each phase. The frequency division is realised by controlling the arrival of the firing pulses to the thyristors gates. Thus, the wave form of the line current is controlled to obtain the desired wave form associated to the desired frequency. Three methods, to achieve the frequency division are discussed. This method of frequency division causes a discontinuity of both of the load and power supply line currents. Thus high harmonic pollution is generated in these currents. The harmonic spectrum depends on the method of realising the frequency division technique. For all ways. The higher harmonic amplitude is the power supply line frequency component. The harmonics in the load line currents cause undesirable operation as torque oscillation for the induction motor. The harmonics in the power supply line currents cause disturbances to the power system and the neighbour loads. That is why the need to filtering the harmonics at each of the load and the power supply line currents is necessary. For the load line currents, a simple and passive filter is inserted between the voltage controller and the motor. This improves the wave from shapes of the load line currents and consequently the electromagnetic torque. to improve the power supply line currents another filtering method is proposed. This is achieved by dividing the total loas into two parts. Each part is fed by a separate voltage controller. as the two voltage controllers operate in parallel, the power supply line current is the sum of the two controller currents. In this case the discontinuity of the line current, due to the frequency division technique. is filled by the combination of the two controller currents. The thyristor gate pulses of each controller are controlled to improve the power supply line current. A study of using the two voltage controller to feed only one load was tried. This causes an improvement.