Universal symmetrising method for current distribution in parallel three=phase inverters - controlling pulse formation w.r.t. shunt or zero current thresholds by supplying corresp. null vectors

摘要

The universal regulating system is for current symmetry within parallel inverters (WRA,WEB) supplying an electric drive. A control device (1) provides setting signals (SW,SV,SU) fed to pulse former stages (3UA,3UB) for controlling switching of the inverters (WRA,WRB). The individual currents at the outputs of the inverters (WRA,WRB) are detected by current converters (8UA,8WB) and fed to comparators (6). The outputs of all 3 comparators are summated and divided by 3 to provide a zero current (iqo). This is compared with the comparator outputs (iqu,iqv,iqw) to provide shunt currents fed to an auxiliary control device (2) between the main control device (1) and the pulse former stages (3UA,3UB). ADVANTAGE - Prevents asymmetrical loading of power semiconductors. Does not require selection of power semiconductor or manipulation switching characteristics of shunt coils.