Privacy-Preserving Adaptive Secondary Control for DC Microgrids With Constant Power Loads

Distributed secondary control has shown great advantages in achieving voltage restoration for dc microgrids. However, the negative impedance characteristic of constant power loads (CPLs) increases the challenges of stability analysis for dc microgrids with CPLs. Most previous researches suppose that the system is stable, or just obtain the stability conditions, which are related with global information. To solve these problems, we propose an adaptive secondary control method to achieve voltage restoration and current sharing without the direct feedback of bus voltage. Each generator can estimate the bus voltage at the previous sampling instant according to local current information and system model of dc microgrids. To obtain the distributed stability conditions, two distributed algorithms are proposed to estimate the sum of currents of the generators and the global load information. One of the distributed estimation algorithms is embedded with a multirate sampling strategy to obtain the sum of currents. The other estimation algorithm is based on the least-squares method to obtain the global load information. White noise is added to the transmitted information of the distributed algorithms to protect the privacy information. Theoretical analysis shows that the proposed methods not only can regulate the bus voltage with privacy preservation but also provide the distributed stability conditions of dc microgrids with CPLs. Finally, several simulation results are given to verify the effectiveness of the proposed methods.