Active front-end optimization using six-pulse rectifiers in multi-motor AC drives applications

This paper presents a method for producing sinusoidal currents in industrial applications with multi-motor AC drives. The system currents´ THD is kept under 5%, and the input power factor is kept above 0.95 throughout the whole operating range. The proposed control scheme uses AC drives with active front-end converters. These are not PWM converters, but phase controlled six-pulse rectifiers using GTO thyristors, and therefore reduce the AC drives´ commutation losses, and increase the converter´s power handling capabilities. The proposed method produces a multi-pulse operation of the AC drives. This is realized by assigning predefined phase control angles to each drive´s rectifier. This induces harmonic cancellation between converters and reduces the total input current distortion. The paper presents the complete analysis of the proposed control scheme, and experimental results used to model the operation of a multi-motor drive. The model is then employed to evaluate the method, and through the results obtained shows the feasibility of the proposed control scheme for multi-motor AC drives.