Capacitor Voltage Control for T-type Alternate Arm Multilevel Converter

T-type alternate arm multilevel converter (T-AAMC) is a cost-effective three-arm multilevel converter with DC fault ride-through capability. The current commutation modulation (CMM) can break the energy balance restriction for T-AAMC with considering the arm inductor. In this paper, the current commutation process for T-AAMC is firstly explored and derived by analytical expressions. Furthermore, the mechanism of the capacitor voltage sag caused by commutation process is clarified, which provides the fundamental to design the controller. Then, the capacitor voltage control (CVC) for T-AAMC is proposed for the capacitor voltage sag to achieve the normal operating in the four quadrants. Finally, the simulation and experimental results are performed to verify the effectiveness of the proposed control strategy.