Modular Multilevel Converter with Thyristor DC-link Switch for Full-torque Variable-speed Drives

卷:9

Article

关键词: PROPULSION;    OPERATION;    ZERO;   

DOI  :  10.17775/CSEEJPES.2021.00500

来源: SCIE

【 摘 要 】

The modular multilevel converter (MMC) is a promising topology for medium-voltage drive applications due to its high-quality output waveforms, low device switching frequency and voltage rating. However, the large cell capacitor voltage ripple is a severe challenge faced by MMC at low motor speeds. Recently, a hybrid MMC (HMMC) topology is proven to be a competitive solution because of its lower cell capacitor voltage ripple and not demonstrating a common-mode voltage (CMV) problem compared with other methods. However, the DC-link switch with IGBT limits HMMC from being applied in high-voltage applications. This paper uses a thyristor instead of IGBT as the DC-link switch. To ensure the thyristor can be softly turned on and safely turned off, a new control scheme is proposed. When using this proposed scheme, HMMC can also tolerate the failure of the thyristor being turned-off without shutting down the system, effectively improving its reliability. The cell capacitor voltage ripple analysis is presented considering the effects of the thyristor switching process. In addition, a decoupled energy balancing control is utilized to suppress the fluctuation of the DC current. Experimental results obtained from a 380 V/7.5 kW downscaled prototype validate the effectiveness of starting up a motor from the standby mode to rated speed applying full-torque.