DC-link Capacitor Voltage Balancing Technique for Four-Level $\pi$-Type Inverter fed PMSM for Marine Propulsion Application

Reliable power quality is one of the crucial aspects in marine electric drive trains. Power quality can be increased by using multilevel inverters instead of two level inverters. Therefore, this article utilizes four-level n-type inverter due to less component configuration. The inverter is required to be supplied from split dc-link with three capacitors in series to provide four voltage levels. Imbalanced voltages of dc-link capacitors produce distorted output voltage waveforms. In order to improve the output voltage levels this article proposes a novel closed loop dc-link voltage balancing strategy. The proposed strategy uses split modulating wave method and can be easily implemented with existing variable carrier based method. A variable carrier is utilized to regulate the voltage of the most sensitive middle capacitor and split modulating waves balances rest of the capacitors. The feasibility of proposed balancing strategy is verified with MATLAB/Simulink tool.