A High‐Resolution Cascaded Multilevel Inverter for STATCOM Applications

Asymmetric cascaded H‐bridge multilevel inverter is well known for generating high‐resolution output voltage levels using a limited number of switches. This paper presents a quaternary asymmetric inverter topology developed for STATCOM applications. Depending on the modulation index, the auxiliary bridges of the converter may exchange power in the opposite direction to the overall converter, posing challenges in maintaining the voltage balance of the floating capacitors. A closed‐loop control strategy is employed to ensure capacitor voltage regulation to compensate for the device losses of the auxiliary H‐bridges. Power required by all the floating capacitors of the auxiliary H‐bridges is supplied from the main bridge dc‐link through a high‐frequency link of negligible rating sharing a common magnetic core and primary winding. The semiconductor losses under STATCOM operation are analyzed and found to be greater than the power absorbed by auxiliary sources across all operating conditions. This enables the adaptation of a unidirectional isolated dc‐dc converter of negligible rating to have power flow from the main bridge to auxiliary bridges, which compensates for voltage sag in auxiliary capacitors because of the system non‐idealities. The proposed inverter topology has been modeled in MATLAB/Simulink and experimentally validated, demonstrating effective capacitor voltage balancing and efficient performance in STATCOM operation.