An inverter with thyristors and antiparallel diodes (voltage valves) connected to a synchronous machine offers the possibility of operating the motor at higher speeds than the so-called current-converter motor - a synchronous motor fed by an inverter with thyristors (current valves) - is able to do. The disadvantage of a more complex run-up performance can be overcome by a control strategy which takes care of the additionally induced free-wheeling diode and machine currents. These currents depend on machine parameters and especially on the control angle as is explained. Digital simulation and results from an experimental drive system verify the calculated characteristics.