Modular Multilevel Converter based Induction Machine drive with Reduced Voltage Ripple across Submodule Capacitor

This paper proposes a half-bridge submodule based modular multilevel converter (MMC) to drive an induction machine (IM). It addresses the issue of high voltage ripple across the submodule capacitor at low operating frequency with reduced component count and no circulating current. A controlled variable current source, derived from a thyristor based rectifier or another MMC, is used as an input to the machine-side MMC for this configuration. The proposed configuration and its control ensure that the peak-to-peak ripple voltage of the submodule capacitor is dependent on the electromagnetic torque only. A detailed discussion on the operation, relevant control strategies, and analysis of proposed IM drive are presented in this paper. The performance of this drive is validated by experiments performed on a laboratory prototype at different operating speeds and various load torques.