This paper deals with a power management mechanism using Modular Multilevel Converter (MMC) with integrated energy storage elements, the typical use of which could be a grid-interface for a photovoltaic park or a charging park for electric vehicles. In comparison with the currently commonly used topologies of MMC, which use submodule DC/DC converters to control the submodule voltages at the half-bridge side and see the energy storage elements as the distributed voltage sources of MMC, the proposed topology in this paper put additionally a buffer capacitor between the submodule halfbridge and the DC/DC converter, taking this capacitor as the direct voltage source of MMC. Consequently, the energy balancing system will be targeted on the energy stored in these buffer capacitors, regarding the power flow gone from these capacitors to the final energy storage elements as disturbances for the controllers. One of the main advantages of this proposal is the healthy operation of MMC under fault-condition of its submodule energy storage elements, which serves to guarantee a stable and robust connection to power grids. Moreover, the power flow of the energy storage elements is free from the energy balancing task and thus can be controlled independently and individually, ranging from zero to the maximum output power of the energy storage elements. This is a beneficial characteristic for a PV park with large scale and various input power of its battery packages or for an EV-charging park to charge different battery packages inside different vehicles with their own best charging profile at the same time within a single MMC.