a wandlervorrichtung and a method for controlling the same

摘要

In a device for converting alternating voltage into direct voltage and conversely having a series connection of at least four units (1-4) each comprising a semiconductor device (10-13) of turn-off type and a diode (14-17) connected in anti-parallel therewith between two poles of a direct voltage side, a flying capacitor (25) is connected between two outer midpoints (24, 26) between two units of the series connection, while the midpoint of the series connection is connected to an alternating voltage phase line (18). An arrangement (27) is adapted to control the units (1-4) depending upon the voltage measured across the flying capacitor and the direction of the current in the alternating voltage phase line for obtaining charging or discharging of the capacitor when achieving an intermediate level of a voltage pulse delivered on the phase output.