Distributed Unified Controller Design for Parallel Battery Storage System in DC Shipboard Microgrid

In this paper, a novel distributed unified controller is designed to solve the problems of unbalanced State of Charge (SoC), unreasonable load current sharing, and unstable DC bus voltage for parallel battery storage systems (BSSs) in DC shipboard microgrid (DC-SMG). Different from the droop-based secondary controller, the designed distributed unified controller is a droop-free primary controller, which can incorporate SoC balancing, current sharing, and voltage regulation functions in the primary control layer. On this basis, each BSS uses an improved dynamic diffusion algorithm (DDA) to iteratively estimate the average information, and completes information exchange by a neighbor-to-neighbor communication network. Furthermore, the small-signal stability, large-signal stability, and global steady-state performance of the system is investigated using eigenvalue analysis, mixed potential theory (MPT), and matrix theory, respectively. Finally, the Matlab/Simulink simulation model and the StarSim HIL experimental platform for DC-SMG are built. The results show that the designed distributed unified controller can simultaneously achieve dynamic SoC balancing, proportional load current sharing, and smooth average bus voltage regulation, and has a faster SoC convergence speed and more stable control effect than the state-of-the-art methods.

I. Introduction

Recently, the global “carbon peak and carbon neutrality” objective has spawned a new round of ship power technology transformation and promoted the transition of the shipping industry to a green and low-carbon direction, which has brought opportunities for the development of new energy ship power systems [1]. However, large-scale access of renewable energy such as solar energy is likely to have an impact on the shipboard power grid. Therefore, it is indispensable to construct a new type of shipboard power system dominated by renewable energy to ensure the efficient consumption of renewable energy. In the existing shipboard power system, the DC shipboard microgrid (DC-SMG) does not require to consider the problems of harmonic suppression, reactive power compensation, and frequency synchronization, and has the advantages of high energy conversion efficiency, strong equipment operation flexibility, and superior fault protection performance, so it has gradually become an important research field for shipboard power systems [2], [3], [4].