Analytical Study of the Inverter Imposed Current Ripple and its Effects on the Performance of Integrated Modular Motor Drives

Integration of the electrical machine and drive system is an ongoing research topic among scholars in both academia and industry with the goal of increasing power density and efficiency to fulfill the requirements of aviation applications. The drive system structure and the modulation scheme impact the stator current ripple which affects torque ripple and efficiency. The case study of this paper is an integrated motor drive system of a 250 kW and 5,000 rpm direct drive surface permanent magnet machine. The imposed current ripple for different three- phase topologies (two-level VSI, and modular single-phase) using different modulation schemes (SVPWM for two-level VSI and Unipolar PWM for single-phase) are analytically studied. It is shown that in a modular single-phase full-bridge topology, the maximum peak to peak value of the current ripple is significantly lower than modular single-phase half-bridge and three-phase SVPWM modulated two-level VSI over the entire operating range. Furthermore, the torque ripple, stator core loss, and winding loss are evaluated for different current profiles through finite element analysis (FEA) simulations.