Submodule for conversion of direct current power and method for updating program for submodule

A submodule for conversion of DC power capable of a being connected in series with other submodules and used for DC-DC conversion, comprising:

• a power switching element for switching DC power supply to convert a source of DC, including voltage transformation;
• a DC capacitor for storing DC power opened or closed by the power switching element;
• a power supply unit for supplying power required to drive the submodule from the DC capacitor;
• a submodule controller for controlling whole operation of the submodule;
• memory for storing data required for operating the submodule controller;
• and
• a communicating unit for performing data communication with an external device;
• wherein the submodule controller performs a program update during a start sequence of the submodule or during a stop sequence thereof, while the DC-DC conversion is operated,
• wherein the start sequence is performed in a passive charging zone of the submodule,
• wherein the power is supplied to the submodule controller when voltage of the DC capacitor in the submodule is charged to a level exceeding a certain voltage at an area of the passive charging zone and the submodule controller for the passive charging zone does not control other components in the submodule to secure enough power supply, and
• wherein the power is supplied to the submodule controller for the stop sequence for a few minutes when the submodule controller for the stop sequence does not control the other components in the submodule to secure the enough power supply.