Mengesha, Mamo (PhD)Abraham, Mesfin2020-10-232023-11-282020-10-232023-11-282017-10http://etd.aau.edu.et/handle/12345678/22951The interest in multi-phase machines for high performance applications has been growing in recent years due to their potential advantages over the conventional three-phase machines. Multi-phase machines have advantages of fault tolerance and higher power capacity at low voltages compared to three-phase machines. Nine-phase brushless DC motor has additional advantages of high torque density, high efficiency and reduced stator current per phase without the need to increase the phase voltage. Sensored control of BLDC machine generally requires measuring the speed and position of rotor by using the sensor. The position sensors make the motor system more complicated, mechanically unreliable and expensive. In this thesis, effective sensorless control of nine-phase BLDC motor using Back-EMF waveform sensing is done. Thus, actual implementation of the motor using mathematical model of the machine and nine-phase inverter function based on the back-EMF sequence generated in the stator windings of nine-phase BLDC motor is simulated with the help of MATLAB Simulink software. For control of the motor PI speed controller is implemented to adjust DC-link voltage based on the error between actual speed and desired speed reference. The controlled gain output of the PI controller is fed to the pulse amplitude modulation controlled DC-link voltage source. The result of the controller is investigated and the speed of the motor for different speed level using MATLAB Simulink software. And the result of the simulated speed response of the controller for different speed has been done and settling time is 0.005sec and rise time is 0.0026sec speed response controller. Phase voltages of the motor controlled based on the back-EMF waveform sequances . switching of nine-phase voltage source inverter controlled has been done efectively based on the back-EMF. The simulation results obtained agree with the design objective.en-USMultiphase machineeighteen-step inverternine phase BLDCMsensorless controlback-EMFzero-cross detectioncommutation logicThesis