Reduction of torque ripple in induction motors by using a modulated rotor

Abstract:
Low torque ripple in electrical machines is generally required to reduce the acoustic noise and the mechanical resonance vibration. The torque quality of an external rotor induction motor is an important part in many electrical drive systems, especially in ventilation systems. The most common methods to reduce the harmonic torques are the proper choice of the number of slots and the skewing of rotor bars. Even if these methods are often used, they affect the average torque value and overall performance of the motor. In this paper an alternative approach to minimize the torque ripple is investigated. An analytical proceeding to design rotors with asymmetrical rotor slot pitch is introduced. The angle modulation known from telecommunications is used for this purpose. A two dimensional (2D) finite element analysis of an external rotor induction motor is also performed. Finally, the measurement results are compared and the effectiveness of the proposed procedure is discussed.