The paper examines the impact of the line impedance of n parallel-connected inverters on the power flow, current distribution and circulating current among the units. Meanwhile, the previous research investigates either the case of inductive or resistive aspect for no more than three inverters connected in parallel. We figure out, for any number n of parallel inverters, the power flow with respect to the coupling impedance that meets the required inverter mode of operation: coupling impedance conditions are established. Furthermore, different line impedance from one inverter to the common point of connection contributes to a non-uniform output current distribution, which might exceed the ratings of the units. In addition, impedance difference from one phase to another of a given inverter induces a circulating current. To avoid such problems, new sinusoidal pulse width modulation (SPWM) strategy where parameters are found analytically is developed. First, a uniform current distribution independently of their number n and their line impedance is achieved. Second, an optimal circulating current with respect to the line impedance of each single unit is attained. Simulation is performed to validate analytical results.

Keywords: Grid-tied, Parallel inverters, Line impedance, Power flow, Uniform current distribution, Optimal circulating current