AC Impedance Measurement Techniques

Naval ship as well as aerospace power systems are incorporating a greater degree of power electronic switching sources and loads. Although these power electronics based components provide exceptional performance, they are prone to instability due to their high efficiency and constant power characteristics which lead to negative impedance. When designing these systems, integrators must consider the impedance versus frequency at a system interface (which designates source and load). Stability criterions 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 suggests several methods for measuring AC impedance including utilization of power converters, induction machines and chopper circuits. Simulation results on an example AC system demonstrate the effectiveness of the proposed methods