DC microgrid consists of cascaded power converters in which the constant power load behaviour of point-of-load converters poses challenging stability issues even if individual converters are stable. In this paper, a robust sliding mode controller has been proposed for DC/DC bidirectional buck-boost converter interfacing storage unit in an islanded DC microgrid environment. The controller is designed to ensure DC bus voltage regulation in the presence of renewable energy source and predominantly constant power loads. The performance of the proposed controller is validated through real-time simulation conducted using OPAL-RT® Digital Simulator. The controller ensures DC bus voltage regulation within tight limits and is robust with respect to wide variations in the renewable energy source power and the load. © 2015 IEEE.