IMPROVED METHOD FOR DETECTING A POWER REVERSAL IN A BI-DIRECTIONAL MODULAR CONVERTER

A method for controlling a modular converter, said modular converter comprising a plurality of M converter cells, each converter cell comprising an AC-to-DC converter, a primary side of which represents a primary side of said converter cell, a DC-to-DC converter, a secondary side of which represents a secondary side of said converter cell; with a secondary side of said AC-to-DC converter and a primary side of said DC-to-DC converter connected in parallel with a first DC-link capacitor, a secondary side of said DC-to-DC converter connected to a second DC-link capacitor; wherein each DC-to-DC converter may be operated in at least a first active operation state, in which electric power may flow into the primary side and out of the secondary side of said DC-to-DC converter; and a second active operation state, in which electric power may flow into the secondary side and out of the primary side of said DC-to-DC converter; the primary sides of the converter cells are connected in series, with a first converter cell connected to a line, preferably a medium voltage line, providing an AC line voltage U(t) having a peak value Û, and an M-th converter cell connected to a ground; comprises the steps of: repeatedly determining a switch-over indicator, switching at least one DC-to-DC converter between first and second operation state if the switch-over indicator fulfils a switch-over condition. In accordance with the invention the switch-over indicator is determined based on one or more of the following quantities, said quantity or quantities preferably obtained by measurement: one or more voltages at one or more first DC-link capacitors, one or more voltages at one or more second DC-link capacitors, a DC-to-DC converter current (/conv) at a point between the first DC-link capacitor and the second DC-link capacitor of at least one converter cell, and/or a load current (/load) at a secondary side of the modular converter. L'invention concerne un procédé de commande d'un convertisseur modulaire, ledit convertisseur modulaire comprenant une pluralité de M cellules de convertisseur, chaque cellule de convertisseur comprenant un convertisseur alternatif-continu dont un côté principal représente un côté primaire de ladite cellule de convertisseur, et un convertisseur continu-continu dont un côté secondaire représente un côté secondaire de ladite cellule de convertisseur ; un côté secondaire dudit convertisseur alternatif-continu et un côté primaire dudit convertisseur continu