HARMONICS AND TORQUE RIPPLE MINIMIZATION USING L-C FILTER FOR BRUSHLESS DC MOTORS

Brushless DC Motors (BLDCM) are widely used in automated industrial applications like Computer Numerical Control (CNC) machinery, aerospace applications and in the field of robotics. The dynamics of this motor should be smooth for many industrial and automated applications and free from unwanted interference. But due high speed switching circuits used in the commutation circuits, the BLDC motor voltage contains harmonics component and this causes high electromagnetic interference problems. During commutation the trapezoidal current pass through each phase causes pulsation in torque during its operation. This work proposes an improved methodology to reduce the high frequency harmonics components and torque ripples using a RC filter connected at the input of the motor. This work is simulated using PSIM and the effect of filter is analyzed with FFT analysis. An experimental setup is developed to analyze the performance of the drive with the proposed system and the experimental outputs were compared with the simulated values and the improvement in performance is analyzed.

INTRODUCTION

The brushless dc motor (BLDCM) has found to be more efficient than the existing DC motor and induction motors Due to the simplicity in control scheme, high power density, reliability, and maintenance free operation, BLDC motors are used in the field of industrial automation, Computer numerical control machines and in the field of robotics. The mechanical losses are minimized since no brushes and no mechanical commutator present in the motor. The dynamics for this motor should be smooth for many industrial and automation applications. Due to the power electronic commutation, the usage of high frequency switching of power devices, imperfections in the stator and the associated control system, the input supply voltage to the motor contains various harmonics components. During its operation, high frequency components present in the voltage input will cause serious electromagnet interference (EMI) problem and the pulsating current input due to electronic commutation causes torque ripple. So an efficient controller is required to reduce the harmonics present in the input voltage to the motor and to reduce the pulsating variation of line current to the motor. 

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