Experimental Verification of Bi-Directional Modular Multilevel Cascaded Converter Suitable for Applying 120-Degree Discontinuous Pulse Width Modulation Maximum

Abstract

Modular Multilevel Cascaded Converters (MMCCs) have advantages in the application of high or medium voltage without transformers. They can also generate high quality voltage with fewer harmonics. Their unique merits make them leading technology candidates for high/medium voltage applications. However, a concern still exists that the number of parts may be increased. In this study, an MMCC topology using high-voltage IGBT (HV-IGBT) with snubber capacitor connected in parallel as a cell module arm is proposed, by which the number of cells can be halved and conduction loss can be significantly reduced owing to the output current flowing through the HV-IGBT in 1/3 of the cycle. Meanwhile, the proposed control stratagem can control the cell capacitor voltage, suppress the HV-IGHT surge voltage, and avoid short-circuiting of the snubber capacitor by circulating current. This study reports the evaluation results of capacitors and the experimental results of bi-directional active power conversion operation.