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.