Energy Efficiency Enhancement in Mini-Hydro-Power Pumping Systems Using the Improved Voltage Balancing of Modular Multilevel Converters

This paper proposes a mathematical estimation-based strategy for Submodule (SM) capacitor voltage balancing in Modular Multilevel Converters (MMCs), with the objective of suppressing circulating currents and improving energy efficiency in hydro pumping applications. The method derives the SM voltage reference from the estimated capacitor energy ripple instead of a fixed capacitor voltage reference, enabling adaptive suppression of circulating currents and improved energy efficiency. Simulation studies confirm that the method effectively balances capacitor voltages, suppresses circulating currents, and enhances current quality. Compared with the conventional balancing scheme, the proposed method reduces the Total Harmonic Distortion (THD) of arm currents from about 11% to 7% and increases converter efficiency from 93% to nearly 98% at rated load. The efficiency improvement becomes more evident under high-load conditions, confirming the scalability and adaptability of the proposed approach across various operating ranges. It enhances converter performance and reliability while significantly improving energy utilization. These advantages make the method a practical and efficient solution for MMC-based hydro pumping systems.