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Distributed DC power systems are becoming increasingly common in advanced automotive systems. Constant power load (CPL) behavior of tightly regulated DC-DC converters in multiconverter power systems is equivalent to the dynamic negative impedance, destabilizing the DC bus and, consequently, the system. Various techniques have been developed to control ideal/lossless converters loaded by CPLs. Loss components significantly enhance the stability of the cascaded converters. In this paper, the effects of parasitics in the behavior of DC-DC converters loaded by CPLs are investigated. Furthermore, the stability of power converters loaded by CPLs in parallel to conventional constant voltage loads in the presence of loss components is analyzed. Design criteria are presented for converter operation in continuous and discontinuous conduction modes, which gives recommendations on the design of multiconverter DC power systems to avoid negative impedance instability. The proposed stable operation criteria are validated with hardware prototypes and simulation analyses.
Date of Publication: June 2008