  The main challenge in using the Modular Multilevel Converter-based
constant-torque variable-speed motor drives is increased sub-module capacitor
voltage ripples (SM-CVR) at lowfundamental frequency operation, due to the
inverse relationship between SM-CVR and operating frequency. To address this
issue, a variable slope trapezoidal circulating current (CC) is injected along
with square wave common-mode voltage (CMV). Compared to sinusoidal CC and
sinusoidal CMV injection, the proposed injection technique can reduce the peak
of the CC in the range of 0% to 50%, resulting in lesser device stress and
improved efficiency. Simulation results of the proposed technique are
presented, and they are further compared with the existing injection techniques
to show the superiority

Systems and Control;Systems and Control