Cascaded H-bridge Converters with Sensorless Voltage Balance through Parallel Branches

Cascaded H-bridge converter (CHBC) enjoys the benefits of modularity and scalability, and is widely applied in photovoltaic power generation, power electronic transformer, static synchronous compensators (STATCOM), and other occasions. However, dc-side capacitor voltage balancing is a technical difficulty in the practical application of CHBC. The traditional software-based balancing methods will cause heavy use of the dc-side voltage sensors and high computational burden on balancing algorithm. In this paper, an effective hardware-based balancing method is proposed to realize capacitor voltages of sub-modules balance by adding balancing arms between sub-modules of CHBC to build capacitors parallel branches. The proposed balancing method balances the capacitor voltages in a voltage sensorless fashion, which translates into the removal of a large number of voltage sensors and great simplification of the control system. In addition, the existence of the parallel branches enables capacitors precharging in a simple way. Finally, the simulation results verify the effectiveness of the proposed balancing strategy in capacitor voltage balancing of CHBCs as a STATCOM.