Control method for avoiding a common-mode shift in the output voltage of three-phase, three-point pulse- controlled converter systems

摘要

The invention relates to a method for controlling a three- phase, three-point pulsed-controlled converter system 3 for which no potential difference occurs between the mains system star point 5 or load neutral point 12 and the intermediate circuit voltage neutral point 15. In this case, according to the invention, in order to form a nominal three-phase vector 27, which is predetermined by a higher-level control unit, within each pulse period, e.g. 44, three switching states are generally used [lacuna] voltage vectors 31, 32, 37 which lie immediately adjacent on the nominal vector 27, for which the sum of the associated input voltages results in the value zero at any instant in time. Furthermore, according to the invention, the switched-on duration of the three-phase vector 31 which is closest to the nominal voltage vector 27 is split symmetrically between the start and end of each pulse period, and the sequence of the two remaining switching states 32 and 37 is interchanged after each pulse period, thus ensuring that the switching frequency fluctuation of the input currents during pulse-controlled rectifier operation, or the output current during pulse- controlled inverter operation of the system, are minimised. IMAGE