Sensorless Speed Control of Brushless DC Motor with Fuzzy Based Estimation

This paper describes a simple way to control the Brush Less DC Motor (BLDCM) for electrical applications. To control this machine it is generally required to measure the speed and position of rotor by using the sensor because the inverter phases, acting at any time, must be commutated depending on the rotor position. The position sensors make the motor system more complicated and mechanically unreliable. A method for the estimation of the speed and rotor position of a BLDCM is presented in this work. Fuzzy based Back EMF observer is employed to estimate the speed by using measurements of the stator line voltage and line current. Most existing sensorless methods of the BLDC motor have low performance at transients or low speed range and occasionally require an additional circuit. To overcome this problem, the estimation of a back-EMF is carried out by fuzzy logic techniques to improve the performance of the system. This method proposes back-EMF observer based on fuzzy function approximation and the system state equation of the BLDC motor. The fuzzy logic technique is used to estimate the speed of the BLDC motor under variable and fixed condition of the back-EMF. Finally, the speed is controlled by using Proportional-Integral (PI) Controller with the help of fuzzy based estimation of the speed and rotor position. Here, fuzzy based estimation of speed and rotor position which is also verified with the sensor, feeds input to the PI controller which does really well for good performance.