Impacts of Inductor Nonlinear Characteristic in Multiconverter Microgrids: Modeling, Analysis, and Mitigation

Powder magnetic materials are excellent alternatives for filter inductors of a power converter due to high saturation flux density and low cost. Unfortunately, inherent soft-saturation nonlinear characteristics of powder magnetic core can deteriorate control performance of the power converter, which has been paid intensive attention to individual grid-connected inverters. However, such impacts on the nonlinear characteristics of filter inductors are merely concerned in multiconverter systems, where the control performance of paralleled converters is more complicated than that of the individual converter. This article investigates and mitigates the impacts on the nonlinear characteristic of filter inductor in multiconverter microgrids so that the comprehensive performance can be improved in a cost-effective way. An average model of the inductor is first established to quantitatively analyze the nonlinear characteristic. Then, an impedance model of a multiconverter microgrid is derived to analyze the effect of the inductor nonlinear characteristic on power control performance. Furthermore, a robust droop control strategy is developed to mitigate the effect of inductor nonlinear characteristics on power control performance. In addition, sensitivity analysis is implemented to assess the immunity capability of the proposed control strategy on the nonlinear inductor. Simulation and experimental results show that the proposed droop control strategy is able to perform desirable power control performance with a sound capability to mitigate the effect of a nonlinear inductor, which thus improves the operation performance and reduces the design cost of multiconverter microgrid.