Fast harmonic analysis method for unbalanced distribution systems

A fast harmonic analysis method for unbalanced radial distribution systems is proposed in this paper. The proposed method is developed based on the exact three-phase component models, frequency-scan formulation and commonly used forward/backward sweep techniques. The backward sweep technique is used to build the relationship between branch currents and bus current injections of a distribution system, and then the forward sweep technique can use the relationship to calculate bus voltages. The forward/backward sweep technique is a powerful method and has been widely used in distribution system analysis; however, it cannot be used for harmonic analysis directly. Therefore, the proposed method designs some specific data formats, embeds them into the commonly used forward/backward sweep techniques and derive some useful formulas to find the effects of system status induced by harmonic pollution. The proposed method is more efficient than the conventional harmonic analysis algorithms, since the time-consuming procedure of the admittance matrix inverse is not necessary in the solution procedure. Test results demonstrate the accuracy and efficiency of the proposed method.