A novel protection scheme for DC microgrid with hierarchical control

Microgrids have gained more popularity with advancement in renewable energy technology, mainly solar. While the boom in renewable technology has provided an alternative solution for energy crisis and depleting conventional sources, their intermittent nature has raised various control and protection issues. In both AC and DC microgrids, protection issues remain similar except the fact that in DC microgrids protection becomes more critical due to absence of natural current zero. This paper proposes a novel adaptive protection strategy, which acclimates as per the system condition and configuration. The protection scheme is designed and developed for a low voltage hierarchical controlled DC microgrid. A three-layer hierarchical control stacked with a local control, an emergency control and a supervisory control is used. Local controllers control the converters associated with the source to achieve source optimization and provide local power flow control. Emergency control is realized with a microgrid protection and control supervisor (MPCS). When fault or sudden large change in load occurs, the stability of system gets critical. Quick and accurate differentiation of normal and abnormal operating conditions becomes essential. The MPCS takes over the control in such situations. The absolute values and rate of change of voltage and current measured at multiple points in the system, helps MPCS to act precisely and quickly. The supervisory control updates MPCS to adapt to the current state of the system with the help of pre-calculated modified fault levels. Texas Instruments' TMS320F28069 digital signal processors (DSP) are utilized for the implementation of proposed microgrid protection scheme.