Stability analysis and nonlinear current-limiting control design for DC micro-grids with CPLs

Authors: Andrei-Constantin Braitor; George C. Konstantopoulos; and Visakan Kadirkamanathan

Published in: IET Smart Grid, 3: 355-366.

Date Published: 21 May 2020


In this study, a DC micro-grid consisting of multiple paralleled energy resources interfaced by both bidirectional AC/DC and DC/DC boost converters and loaded by a constant power load (CPL) is investigated. By considering the generic dq transformation of the AC/DC converters' dynamics and the accurate nonlinear model of the DC/DC converters, two novel control schemes are presented for each converter-interfaced unit to guarantee load voltage regulation, power sharing and closed-loop system stability. This novel framework incorporates the widely adopted droop control and using input-to-state stability theory, it is proven that each converter guarantees a desired current limitation without the need for cascaded control and saturation blocks. Sufficient conditions to ensure closed-loop system stability are analytically obtained and tested for different operation scenarios. The system stability is further analysed from a graphical perspective, providing valuable insights of the CPL's influence onto the system performance and stability. The proposed control performance and the theoretical analysis are first validated by simulating a three-phase AC/DC converter in parallel with a bidirectional DC/DC boost converter feeding a CPL in comparison with the cascaded PI control technique. Finally, experimental results are also provided to demonstrate the effectiveness of the proposed control approach on a real testbed.

Insights for EnergyREV:

A rigorous primary control design can enable the bidirectional power flow for energy storage systems and interlinking converter applications, in both AC and DC microgrids. Visualisation or graphical analysis can provide extra information on the limits in operating the microgrid, in presence of active loads. Experimental testing improves the understanding of the microgrid system response when subjected to changes of the load power demand or operating near the technical limits.