Reduction of Torque Ripple in Trapezoidal PMSM using Multilevel Inverter

Permanent Magnet Brushless DC motors are used wide applications in industries due to their high power density and easy to control. These motors are generally controlled using a three phase power semiconductor bridge. For starting and to provide proper commutation sequence to turn on the power devices in the inverter bridge the rotor position sensors are required. Based on the rotor position, the power devices are commutated. To achieve preferred level of performance the motor requires suitable controller. Permanent magnet motors are usually achieving the speed control by using proportional integral controller. BLDC motor drive uses one or more sensors giving positional information to keep synchronization. It results in a higher drive cost due to sensor wiring and implementation in the motor. Also, sensors cannot be used in applications like the rotor is in closed housing and the motor is immersed in a liquid. Therefore, for cost and technical reasons, the BLDC sensor less drive is an essential capability of a brushless motor controller. Implementations of sensor less BLDC control with the lowest possible system cost is essential for maintaining the highest performance. This paper shows that the torque produced by the BLDC motors with trapezoidal Back EMF is constant under ideal condition. Due to freewheeling torque ripples are produced which are to be either eliminated or reduced. This paper proposes, a five level diode clamped multilevel inverter to reduce the torque ripple and the same was simulated using MATLAB software.