Naval ships 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 that can exhibit negative impedance nature at certain frequencies. When designing these systems, 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 impedances 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 an unbalanced line-to-line current between two lines of the ac system, all impedance information in the traditional synchronous reference frame d−q model can be determined. For medium-voltage systems, the proposed technique is simpler and less costly than having an injection circuit for each phase. Since the current injection is between only two phase lines, the proposed measurement device can be used for both ac and dc interfaces. Simulation and laboratory measurements demonstrate the effectiveness of this new technique.Index Terms-Impedance measurement, power conversion, power system stability, power system testing.
are developed for distributed systems with constant power loads to guarantee stability during large disturbances. The criteria place design constraints on the Input filter parameters, such as the Q factor, and constraints on the amount of "ideal" constant power load that a system can support. The crlteria are based on Lyapunov stability theory, mixed potential functions, and the existence of equilibrium points. The analytical criteria are validated by means of computer simulations Abstroet-Design oriented criteria
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.
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