Hybrid three-phase load flow method for ungrounded distribution systems

This paper proposes a hybrid three-phase load flow method for ungrounded distribution systems. Based on topology connectivity analysis, the system is partitioned into a mainline system and multiple tap systems. A Newton method with constant admittance matrix is used to solve the mainline system, such that zero impedance branches are merged into adjacent impedance branches to be considered, and constant active-power and voltage-magnitude (PV) buses with three-phase balanced voltages are transformed into single-phase PV buses to be modeled. A backward/forward sweep with loop compensation is used to solve the tap systems, such that a transformer and a voltage regulator is modeled using line-to-line voltages, a distribution line is simplified as a series branch, and loop compensation current is initialized based on loop downstream loads and the impedances of loop paths. Test results of sample systems are given to demonstrate the effectiveness of the proposed method.