Patent ID: 8390259
Filing Date: 2013-03-05
Classification: H02M

Abstract:
1. A method for charging and/or discharging energy storage devices of a multilevel converter including at least one phase module branch with a series circuit of submodules each having at least one power semiconductor circuit for turning on or off an energy storage device connected in parallel with the power semiconductor circuit and a submodule sensor for detecting an energy storage actual value, the method comprising the following steps: upon obtaining an energy change state, determining if turned-on energy storage devices of a phase module branch can be charged or discharged; selecting the next energy storage device to be switched in each phase module branch with a predetermined logic in dependence on the energy change state; forming a sum of all turned-on energy storage actual values to obtain an energy storage summation actual value; determining a difference between a predetermined phase module branch energy desired value and the energy storage summation actual value to obtain an energy difference value; and defining a switching instant of the selected energy storage device if a magnitude of the energy difference value or a magnitude of a quantity derived from the energy difference value exceeds a magnitude of a switching threshold value.