An Innovative Single-Cell-Based Injection Method to Improve Efficiency and Reliability of MMC with Low Implementation Burden

Modular multilevel converters are increasingly gaining popularity in various high-voltage and high-power applications. However, their operation poses some technical challenges in implementing the control system, including issues, such as balancing submodule capacitor voltages and mitigating circulating currents. The presence of circulating currents leads to additional power losses, increases thermal stress on the power devices, and shortens their lifetime. This article introduces an innovative control technique to eliminate circulating currents by injecting a low-frequency alternating signal into a single submodule of each converter arm. The proposed method not only addresses circulating current mitigation but is also able to reduce capacitor voltage ripple and peak arm current, thereby enhancing the overall converter's lifespan and efficiency. Results of experimental tests on a seven-level converter are presented to prove the effectiveness of the proposed technique and compare its performance with existing state-of-the-art approaches.