Design of Ultra Low acoustic Noise and High Power Density Direct Drive Machines with Double Rotor and Toroidally Wound Structure

According to downsizing the motion applications, high torque and power density are the most serious requirements for electric machines. Double rotor and toroidally winding permanent magnet motor is proposed to solve the problem and it is suitable for direct drive system. But it has a large cogging torque that generates the large acoustic noise. In this paper, we design the direct drive IPM motor and discuss the design method of double rotor and toroidally winding permanent magnet motor for improving the acoustic noise. We show the stator design to minimizing the cogging torque and IPMSM rotor design for sinusoidal back-EMF waveform. We discuss the FEA results and the experimental results of prototype motor. We designed 1.25kW, 50Nm prototype motor. In our experiments, the prototype motor achieved 50% higher power density and 5dB improvement of acoustic noise compared with the conventional type.