Modular Multilevel Converter and Parallel Hybrid Converter Based Open-End Windings AC Machine Drive for Wide Speed Range

The parallel-hybrid converter (PHC) is a potential alternative to the modular multilevel converter (MMC) for medium voltage (MV) drive applications due to its remarkable features of lower static energy storage, fewer devices, and zero voltage switching. Interestingly, for PHC-based variable speed drives, the submodule (SM) capacitor voltage ripple (CVR) is not highly affected by the operating speed, unlike MMC drives. However, in PHC drives, the current shoot-through in the DC-link is inevitable for variable motor voltage when the DC voltage source is stiff, which restricts the operating speed range of the drive. Hence, this article proposes a transformerless MMC-PHC drive configuration for open-end stator winding AC machines (OEWM). The MMC acts as an active front-end converter that generates variable DC-link voltage to feed the motor-side converter while maintaining grid-side control targets. A coordinated control strategy between the PHC and MMC sides is proposed to achieve their control targets. The proposed drive configuration also offers regenerative operation. A comparative static energy storage analysis between the proposed and existing state-of-the-art MV drives is presented to verify its effectiveness. The proposed configuration and control strategy are evaluated for different operating conditions, including dynamic load change and regenerative operation, using both simulation and experimental studies.