VOLTAGE SOURCE CONVERTER GENERATING A PULSE TRAIN USING TWO VOLTAGE LEVELS

摘要

A voltage source converter (10) comprises a first converter arm (ua) connected between a junction (j) and a first DC terminal (DC1), a second converter arm (la) connected between the junction and a second DC terminal (DC2) and a string of capacitors (C1, C2) connected between the DC terminals. The arms (ua, la) comprise cells (Cua1, Cua2, Cua3, Cua4, Cla1, Cla2, Cla3, Cla4). The converter comprises a control unit (12) controlling a group of cells (Cua1, Cua2, Cua3, Cua4) used in the transition for commutating a current running through one of the arms (ua), where the group comprises the cells of this arm. In this control, the control unit (12) obtains values of a current (I_DCL) running between string of capacitor and the converter arm and inserts or bypasses a cell (Cua4) of the group selected to be used last for reaching one of the levels when the current is at a zero level.