Design and Control of High-Performance Modular Hybrid Asymmetrical Cascade Multilevel Inverters

The paper focuses on the active balance of modular hybrid asymmetrical cascade multilevel drives. It investigates special configurations where the high-voltage cell can be operated at low-switching frequency, while correcting the energy imbalances of the low-voltage cells. Among these, it proposes to use configurations with no more than two types of cells and switching devices for modularity. It proposes a high-dynamic performance active balance scheme that decouples the correction of the different imbalances. This allows fast control of the load, while maximizing the inverter voltage use, which results in a higher energy efficiency. An optimal feedback is proposed to correct phase imbalances through the control of the common mode of the low-voltage cells. The effectiveness of the proposed concepts is validated experimentally on a multilevel drive.