Design and control of high performance modular hybrid asymmetrical cascade multilevel inverters with active voltage balance and low losses

The paper focuses on the design and active balance of modular hybrid asymmetrical cascade multilevel inverters. 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.