We propose a battery replacement strategy to increase the efficiency of chargers and save drivers' time at a charging station of plug-in hybrid electric vehicles (PHEVs). With the battery replacement strategy, we optimize the scheduling for the operations of chargers in a charging station. The scheduling objectives are to minimize the power consumption cost and to allow as many PHEVs to be served as possible. Besides, we quantitatively analyze the impact of imperfect data communication on the scheduling performance. Furthermore, we formulate and solve a multi-stage stochastic programming model to minimize the power supply cost for the benefit of the grid operator. Renewable source generation as well as utilization of energy storage device are integrated into the supply optimization problem.

Optimizations of power consumption and supply in the smart grid : analysis of the impact of data communication reliability

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Medium Access Control is an important component in cognitive radio that allow secondary users to identify and access spectrum opportunity without interfering with primary users. In this paper, a queueing model to analyze the performances of the secondary users in a cognitive radio network is presented. The queueing model considers the transmissions of a secondary system where a Medium Access Control algorithm is used to enable the secondary users to sense and access the channels. Also, a simple scheduler is employed to assign transmission time slots to the secondary users. Because the value of the system parameters can be perturbed and cannot be determined precisely, the analysis is extended to take uncertainty into account. In this case, a robust optimization method to study the Markov chain with uncertainty is applied to obtain the stationary probabilities of the queueing model under uncertainty. The lower and upper bounds of performance measures are obtained and compared with the nominal value. Copyright © 2012 John Wiley & Sons, Ltd.