Ac impedance measurement by line-to-line injected current

Naval ship as well as aerospace power systems are incorporating a greater degree of power electronic switching sources and loads. Although these components provide exceptional performance, they are prone to instability due to their high efficiency and constant power characteristics which lead to a negative impedance nature. When designing these systems, system integrators must consider the impedance versus frequency at an interface (which designates source and load). Stability criteria have been developed in terms of source and load impedance for both DC and AC systems and it is often helpful to have techniques for impedance measurement. For DC systems, the measurement techniques have been well established. This paper introduces a new method of impedance measurement for three-phase AC systems. By injecting a line-to-line (unbalanced without zero sequence) current between two lines of the AC system, all impedance information may be determined. Since the current injection is line-to-line, the measurement device may be used for AC or DC interfaces. Simulation and laboratory measurements demonstrate the effectiveness of this new technique