US Patent 7589984 Method for starting pulse width modulation

A method for starting the modulation of a frequency converter, which method comprises the steps of receiving reference voltages (sa, sb, sc; Uref), generating output switch commands from the reference voltages. The generation of output switch commands comprises further a step, in which the ratio (dz) of active time (T0+) in a modulation period (Ts) of selected zero vector and the total active time (T0++T0−) of zero vectors in a modulation period is changed from a first predetermined ratio, which is substantially 0 or 1, to a second predetermined ratio, which is substantially 0.5.