Microcontroller based open loop scaler speed control of three-phase induction motor

Induction motor adjustable speed drives widely used in current industry because of the fact that it has as a low cost, less necessity of maintenance, reliability and high efficiency. As it is known, inverters are the most essential part of induction motor drive, used for converting direct voltage into alternating voltage and controlling its amplitude and frequency as well. Various PWM techniques are used to implement for these purposes.Inverters are classified two main classes depending on feeding methods as Voltage Source Inverter (VSI) and Current Source Inverter (CSI). VSI generally used for speed control of induction motor. The Pulse Width Modulation (PWM) techniques used in control of inverter affect directly output performance of it. The best known among these PWM techniques is Sinusoidal PWM (SPWM). However, space vector PWM (SVPWM) becomes the best used PWM technique thanks to developments of microprocessor technology currently. This technique, comparing to SPWM, provides specific advantages such as better direct current (DC) bus utilization and harmonic performance as well as reduction of switching loss.In this thesis, microcontroller based open loop scalar speed control of a typical three-phase induction motor is implemented experimentally by using SPWM and SVPWM methods by means of VSI. Phase voltage and line currents at the output of inverter are sampled for both techniques by using voltage and current Hall-effect sensors. Harmonic distribution, Total Harmonic Distortion (THD) and amplitude of fundamental waves are compared against each other by way of obtained results. In consequence of experimental studies, it is seen that SVPWM has better harmonic performance and DC bus voltage utilization than SPWM