20-07-2012, 11:48 AM
Speed control of three phase induction motor using single phase supply with fuzzy logic
Abstract
Majority of industrial drives use electric motors, since they are controllable and readily available. In practice, most of these drives are based on AC induction motor because these motors are rugged, reliable, and relatively inexpensive. The proposed technique of single phase to three phase conversion has a wide range of applications in rural areas and also in industries where three phase equipment or motors are to be operated from the easily available single phase supply. These converters are excellent choice for situations where three phase power supply is not available. The added advantage is that the three phase motor is more efficient and economical than the single phase motor. Also the starting current in three phase motor is less severe than in single phase motor. This needs a strong, efficient cost effective and high quality single phase to three phase conversion. Advanced PWM techniques are employed to guarantee high quality output voltage with reduced harmonics and sinusoidal input current irrespective of the load.
The operation is based on variable turn-on time. Equal Area Criteria (EAC) is applied to the discontinuous current operation. To obtain high quality output voltage, double edge modulated sine wave PWM technique is implemented for three phase inverter. From experimental results obtained on a laboratory prototype it can be concluded that input power factor remains nearly unity for any variations in the load or speed. Thus three phase ac drives using single phase supply with improved power factor is an approach to implement high frequency induction boosting along with the three phase PWM inverter for controlling the speed of three phase induction motor by maintaining v/f ratio at constant value. This scheme can be used in lathe machines, small cranes, lifts etc, which are frequently switched ON and OFF1.
In the prototype model we used a micro controller to generate the PWM pulses and to adjust the speed according to the feedback. An optical sensor with slotted wheel is used to measure the speed. MOSFETS are used to drive the 3ph motor. Fuzzy logic is used to maintain the speed in closed loop.
[img]Block diagram:[/img]