Fuzzysmc based Speed Control of BLDC Motor

Abstract

DC motors are popular in industry. Owing to benefits like higher starting torque, variable speeds with varying input voltage and cheaper to control than AC but they suffer from certain drawbacks due to the presence of commutator and brushes. On the other hand, a BLDC motor doesn't have commutator and brushes and therefore has many advantages over normal dc motor. BLDC motor has very vast speed range but its speed control is difficult. In literature, there are many control techniques reported to control speed. This paper presents FUZZYSMC based speed control of BLDC motor, by combining the beneficial features of both sliding mode control and fuzzy logic. This design is compared with PI controller. MATLAB Simulink model is developed for both the control strategies for different loading conditions. System is tested for various parameter changes and accordingly speed response is observed. From simulation it is evident that, FUZZYSMC controller is better than PI controller in terms of rise time, settling time etc. Keywords-BLDC motor; sliding mode control; fuzzy logic;PI controller. I INTRODUCTION A brushless dc motor is a permanent magnet synchronous motor that has trapezoidal back emf. It possess same characteristics as that of dc motor. Due to absence of brushes and commutator, BLDC motor has many benefits than DC motor, such as high efficiency, faster acceleration, no sparking, less maintenance and longer life. For commutation purpose rotor sensors are employed. Speed control is very important part in BLDC motor. It can be done by using different controllers like PI [16], PID [2], and SMC [14], FUZZY [15] etc. Most popular of these controllers is PI controller. The control system used for regulating speed should ensure that the steady state error is small and the transient response is also satisfactory. The speed of motor is largely affected by varying load conditions. It is thus the duty of a controller to maintain the speed regulated to the desired value. As the load on the motor changes, the PI controller parameters are needed to be retuned to give the same performance. However, a robust control like Sliding Mode is able to deliver the same performance in the event of changing load conditions. This paper presents combination of FUZZYSMC controller which takes into account advantages of both fuzzy and SMC, and makes easy operation of BLDC motor for various speeds. It is then compared with conventional PI controller. II VSI FED BLDC MOTOR A brushless dc motor with voltage source inverter is shown in fig (1).For commutation purpose rotor sensors are employed. According to rotor position, coils are energized in specific sequence to run the motor [2]. The stator winding current pulses are shown in Fig. (2). Currents are placed where EMF induced is greatest and constant [11]. By way of alternative turning on and off the thyristors, stator current follows the reference current. According to faradays law of electromagnetic induction, there is interaction between permanent magnet rotor flux and flux produced by stator coil, which forms torque. This torque shifts Fig.1 Fig.2