Method for pulsing the current of an invertor for supplying a rotating-field machine in the starting range

摘要

In a method for pulsing the current of the invertor, which is driven in a three-phase bridge circuit, of a converter having a DC intermediate circuit for supplying a rotating-field machine in the starting range, which machine is operated in a torque-controlled manner at a variable speed, a reference function being compared with a triangular-waveform sampling function and, depending on the mathematical sign obtained, with a duty ratio which is dependent on the phase angle of the desired current value vector, control signals being released for the thyristors of two branches, which alternate in the current flow, of one bridge half of the invertor for the inlet flow and reverse flow alternately, while the thyristor of one branch of the other bridge half of the invertor is turned on continuously for the return flow or the inlet flow during a phase-angle interval of 60 DEG of the desired current value vector, the object exists of achieving a rotation of the actual current value vector which is as uniform as possible with an identical vector length of the determined vector. This is achieved in that a non-linear function: IMAGE where psi w = psi w (t) = phase angle of the desired value vector is used as a reference function for in each case 60 DEG , the sampling function (D( psi t)) representing a preferably triangular function, varying linearly between 0 and 1 and the intermediate circuit id being modulated in this rotation cycle interval of 60 DEG in accordance with the relationship IMAGE by controlling the rectifier on the network-side invertor of the converter.