A Modular Multilevel Converter with Integrated Composite Energy Storage for Ship MVDC Electric Propulsion System

In order to satisfy the demands of ship high-power electric propulsion system and energy storage system of a medium voltage direct current (MVDC) based ship integrated power system (IPS), a modular multilevel converter with integrated composite energy storage (MMC-ICES) is proposed in this paper. In order to pursue both fast power response and longtime power supply, both batteries and super-capacitors are integrated into the MMC to form a composite energy storage. Therefore, it can not only compensate the pulse power of high-energy equipment in a ship, solve the low-frequency voltage fluctuation problem of sub-module capacitors when the MMC drives a propulsion motor under low speed high torque condition, but also provide emergency power supply under ship grid fault condition. The decoupled control method is discussed in detail and verified by simulation results in this paper.