Paralleling of 3-phase 4-wire DC-AC Inverters Using Repetitive Control

Constant frequency inverters, such as the 60 Hz 120 V UPS or the 208 V 3-phase power system may be paralleled with the utility for backup power or paralleled with similar supplies to increase output capabilities. Previous research has addressed paralleling 3-phase 4-wire inverters. This paper will examine the parallel operation of 2 similar 3-phase 4-wire inverters using repetitive control. Repetitive control is a technique which takes advantage of the fixed frequency to reduce periodic disturbances. This type of control provides further benefits when paralleling supplies.