MicroGrid (MG) is a key component for future Smart Grid (SG) deployment with high potentials. Balancing the supply and demand of energy is one of the most important goals of MG management. In this paper, the authors explore effective schemes for Quality-of-Usage (QoU) guarantees for local residents in an MG, under randomness in both electricity supply and demand. The MicroGrid Control Center (MGCC) aims to maintain the QoU blocking probability around a target value by serving or blocking QoU requests. The problem is formulated as a queue stability problem by introducing the concept of a QoU blocking virtual queue.