Stable and Optimal Load Sharing of Multiple PMSGs in an Islanded DC Microgrid

For permanent magnet synchronous generators (PMSGs) based dc microgrids working autonomously, load sharing among multiple PMSGs is necessary when the available wind power is more than the load demand. During the load-sharing process, PMSG may prone to instability due to possible over deceleration. To address this issue, this paper presents a new distributed control scheme, which can achieve stable and optimal load sharing among multiple PMSGs in a dc microgrid. This scheme has a two-layer structure. Based on the distributed model predictive control approach, the upper layer controllers coordinate the operation of parallel-connected grid-side converters, thus providing power references for each PMSG. The computed power references are sent to the lower layer PMSG controllers for execution. The salient feature of this scheme is that by incorporating the rotor kinetic energy and the generation margin into the controller design, it not only achieves the optimal load sharing, but also ensures stable operation of all PMSGs. Simulation results verify the effectiveness of the proposed scheme.