Modulation Coordinated Voltage Balance Strategy for a Single-Phase Nine-Level T-type Converter

This paper presents a single-phase nine-level T-type converter composed of stackable ac-dc-ac three-leg converter blocks. Several such blocks, each containing two T-type legs and one common leg are connected in series on their ac sides to obtain transformerless high voltage ac interfaces. The proposed converter can provide up to nine levels of sinusoidal voltage to the load at an adjustable amplitude and fixed frequency. However, the capacitor voltages imbalance resulted from parameter mismatch is an issue that should be carefully considered. To balance the capacitor voltages, a modulation coordinated strategy is proposed. Simulation results based on MATLAB/Simulink verify the effectiveness of the topology.