On the Use of Nonlinear Inductor to Enhance the Stability of DC Distribution Networks

Typical dc distribution networks contain source-interface DC-DC converters for feeding constant power loads (CPLs). Instability may arise if the interaction between the output impedance of the converters and the input impedance of the CPLs does not satisfy stability criteria. A simple technique that aims to deal with such issue is proposed. Instead of shaping the network characteristics with sophisticated control laws or introducing passive or active damping, the proposed idea is based on using an output filter with nonlinear inductor in the converter to enhance small-signal and large-signal stabilities. First, the eigenvalues of the Jacobian at the equilibrium points can be maintained in the left half plane. Second, the system state can always be reverted to the target operating point after large-signal perturbation. Furthermore, the physical size of the nonlinear inductor is comparable with that of the fixed-value inductor in the output filter without sacrificing ripple current requirement. The proposed method has been evaluated on a downscaled system with the power level of 80W and bus voltage of 24V. The experimental results are in good agreement with the theoretical predictions.