Mitigation of destabilising effect of CPLs in island DC micro-grid using non-linear control

In recent years DC micro-grid has been widely accepted as one of the promising solutions to integrate renewable energy sources and to supply power to critical loads such as data centres, remote villages and communication stations. However, DC micro-grid has a fundamental stability challenge due to constant power load (CPL) characteristics of point-of-load converters, which introduce destabilising effect in the system. This study presents a sliding mode control based non-linear control scheme for a solar photo-voltaic based DC micro-grid in the presence of CPLs. The objective of the proposed control scheme is to tightly regulate the DC bus voltage and mitigate the destabilising effects of CPLs. The stability of the system is analytically established and a limit of CPL is obtained. Furthermore, a charging/discharging algorithm is implemented for battery bank interfacing bidirectional converter which facilitates three modes charging namely constant current, constant voltage, and float mode, to enhance the battery life. The validation of the effectiveness of the proposed scheme is done through simulation and experimental results. It is found that the proposed control scheme ensures desired operation of the DC micro-grid under various operating modes and maintains system stability with CPL under variations in the primary resource and load demand.