DETAILED EVALUATION FOR THE POWER FLOW EFFECTS OF NONLINEAR CIRCUIT ELEMENTS IN THREE-PHASE NETWORKS WITHOUT NEUTRAL

摘要

Undesired effects produced by the nonlinear characteristic loads connected to the power grid are increasingly present as a result of power electronics, which are prevalent in today's domestic and industrial use. In that sense, the present contribution tries to make a step further in the assessment of the parasitic power circulation of the active and reactive power due to the presence of harmonic content, in both current and voltage waveforms generated by distorting circuit elements. The background of our approach rests on the innovative theory proposed by Professor Tugulea in the mid 1980s, according to which a parasitic power flow (non-symmetry and residual) originates from the nonlinear consumer towards the linear ones. That effect produces both power losses on the line and billing issues by overcharging the balanced and linear consumers. The paper focuses on the residual (distorting) active and reactive power circulation throughout an idealized three-phase power grid without neutral. Trying to generalize the aforementioned theory, we consider two distorting three-phase loads (instead of one) connected to an idealized grid. Two nonlinear single-phase elements of noticeable different ampere-volt characteristics are present on phase one of both three-phase loads. The goal of the paper is to find a way to predict the actual residual (distortion) active/reactive power flow direction, involving an exchange between the distorting single-phase elements, having as starting point the ampere-volt characteristics assumed on an analytical form. Four test-circuits are proposed and analyzed in view of a complete non-symmetry and residual (distortion) power flow assessment, proving that all the possible cases generated vs. absorbed are possible in the case of the less distorting single-phase element of the two. Results are then discussed and compared with the less complex case results of the three-phase networks provided with zero impedance neutral conductor.