Enhancing Stability and Performance of DC Microgrid: A Coordinated Impedance Reshaping Controller Design Approach

Constant power loads (CPLs) are converter-based loads that cause overloading or underloading of specific components in the DC Microgrid (DC MG) system, there by exacerbating stability issues. Several control methods, however, solved this instability by modifying the characteristics of either the source output impedance (SOI) or the load input impedance (LII) of subsystems of the DC MG. Consequently, the Cascaded System (CS) based DC MG control scheme, which simultaneously modifies SOI and LII is barely reported in the scientific literature. This article proposes Decentralized Coordinated Control (DCC), a modification of SOI and LII as a solution to aforementioned issues. First, equivalent SOI and LII of source and load subsystems are obtained using the small signal modeling of DC-DC converters. The open-loop gain transfer functions are then derived to define the boundary that decide on which side impedance should be modified. The presented control stabilizes the system without any delay, and also prevents performance degradation. Finally, various case scenarios are used to verify the effectiveness of the proposed DCC scheme and it is also validated with the laboratory prototype setup. Results showed that the ripple in bus voltage decreased from 0.65% to 0.3% when reshaping technique was applied. And the settling duration of DC bus voltage and current were lowered from 0.025 s and 0.16 s to 0.012 s and 0.1 s, respectively which shows notable enhancement in stability and performance of the DC MG.