Asymmetrical three-phase load-flow study based on symmetrical component theory

For asymmetrical three-phase load-flow study, two methods based on symmetrical component theory, the bus admittance method and the decoupling compensation method, are proposed. By using the decoupling feature of symmetrical-element models in a positive-negative-zero sequence reference frame, such as those of generators and transformers, the bus admittance method can obviously increase the speed of three-phase load flow computation without losing its accuracy. By further using the weak coupling feature of the asymmetrical transmission line model in a positive-negative-zero sequence reference frame, the decoupling compensation method breaks the three-phase coupled model into three sequence-decoupled models with the injection of certain compensation currents into both terminal buses of the line, and thus opens up a way to the utilisation of parallel processing. The validity of these methods is verified by numerical examples.