Microcontroller Based Space Vector Pulse Width Modulation Speed Control of Three-phase Induction Motor

Three-phase induction motors are often times classified as almost constant speed motors due to the less than 5% slip its normal operation is confined to, and it can be challenging to vary the speed without affecting the motor's efficiency. This is because adjusting any one parameter will cause changes in the remaining parameters and affect the entire machine's output. Speed control has been achieved by adjusting the parameters of the rotor or stator to obtain the desired speed range of the motor's shaft. For the stator, the input voltage, frequency, or the number of poles would have to be adjusted and for the rotor, an external resistance can be added or inject slip frequency voltage in the rotor circuit. However, all these methods have their disadvantages and shortcomings as manipulating just one parameter will cause instability within the machine. As such, the constant voltage-frequency (v/f) ratio technique is deemed the most suitable method since it offers high efficiency and is cost effective. This research examines the use of microcontroller-based three-phase Space Vector Pulse Width Modulation (SVPWM) to obtain a constant v/f ratio which will be used to control the speed of a three-phase induction motor. This technique demonstrated control of the speed by varying the frequency relative to voltage. Low frequency and low voltage decrease the speed while high frequency and voltage increase the speed.