Loss Minimization Technique in Scalar-Controlled Induction Motors
Journal Title: International Journal of engineering Research and Applications - Year 2017, Vol 7, Issue 8
Abstract
Core losses are a menace to 3-Phase Induction Motors (3PHIM) and can only be taken care of by adjusting their voltage/frequency ratios using an efficient Voltage Source Inverter (VSI) like the MCT-Inverter. Scalarcontrolled induction motors have their speeds controlled by controlling their stator voltages and frequencies in such a way that the ratio of the stator voltage to the frequency is always kept constant. The drive technology of most scalar-controlled 3-phase induction motors utilizes Voltage Source Inverters such as IGBT-Inverter to achieve variable voltage variable frequency. This scheme is considered to save energy in electrical drive, especially when IGBT-Inverter is used to implement variable voltage variable frequency. However, more energy savings and less energy losses are still possible when IGBT is replaced with Mos-Controlled Thyristor (MCT), as the switching device. This is because of the sterling characteristics of MCT as compared with IGBT. Again, this is unlike vector control methods where thyristor can be fired to bring about a change in speed. In this research, a new switching device called Mos-Controlled Thyristor (MCT) for minimizing losses in scalarcontrolled induction motors is introduced. Based on the new switching device and AT89C52 microcontroller, an enhanced frequency drive for controlling the speed and torque of 3-phase 15kW squirrel cage induction motor is modeled. Different voltages ranging from 342V to 415V and frequencies ranging from 50Hz to 60Hz are used in a systematic manner to simulate the system based on the new switching device. The simulation program is written in C language and tested with Proteus 7.6 simulation software. Voltage and frequency have significant impact on the actual speed and torque of the motor. Simulation results show that with the new model, the torque (56.66Nm) developed by the motor which is constant throughout each speed range is directly proportional to the ratio (6.7) of the applied voltage and the frequency of the supply and the selected speeds (1450, 1510, 1570, 1630, 1690 and 1750 rpm) are locked irrespective of change in load. This is unlike other models where magnetic saturation and conduction drop of IGBT lead to voltage/frequency imbalance resulting in excessive drawing of current by the motor and core losses. Comparison of the system with other speed control techniques shows improved energy-saving, cost effectiveness and safety in operation. Thus, Volts per Hertz speed control method based on MCT is a better alternative to other well known methods in speed control and loss minimization of three-phase induction motors.
Authors and Affiliations
Engr. E. J. Nnake, Engr. Dr. C. B. Mbachu
Keywords
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- EP ID EP391970
- DOI 10.9790/9622-0708031419.
- Views 77
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