Parallel Hybrid Converter-Based Adjustable Speed Drives Using Third Harmonic Voltage Injection Technique

The modular multilevel converter (MMC) is widely preferred in medium voltage adjustable speed drives (ASD) due to its modularity and efficiency. However, the MMC drives face high ripple voltage across the submodule (SM) capacitor during low-speed operation and require high energy storage. A parallel hybrid converter (PHC) based ASD is a potential alternative to MMC in terms of energy storage requirement. In addition, SMs ripple voltage of PHC drive is independent of operating speed. However, the PHC has a strong coupling between the ac side voltage and dc side voltage. In order to achieve the decoupled and variable ac voltage for ASD a third harmonic voltage injection (THVI) technique is proposed. The performance of the proposed technique is verified using the simulation study and further validated using the experimental prototype.