Optimal charging strategies of plug-in electric vehicles for minimizing load variance within smart grids

With serious concerns on global warming and energy crisis, there are plenty of motivations for developing and commercializing plug-in electric vehicles (PEVs). It is believed that substitution of PEVs for conventional fuel vehicles can help reduce the greenhouse gases emission, increase the energy efficiency, enhance the integration of renewable energy, and so forth. At the same time, the impact of PEVs as an emerging electrical load for power grid has drawn increasing attention most recently. The possible challenge for power grids lies in that the penetration of large number of PEVs may trigger extreme surges in demand at rush hours, and therefore, harm the stability and security of the existing power grids. Nevertheless, there are also potential opportunities for power grids. An optimal scenario is to dig the potential of PEVs as moveable energy storage devices, which means PEVs withdrawing electricity from grid at off-peak hours and then feeding back energy deposited in the onboard batteries to grid at peak hours. This concept is also termed as vehicle-to-grid (V2G) technology. The key to the implementation of V2G is how to effectively integrate information into energy conversion, transmission and distribution. V2G should be carried out within the framework of smart grid, so that the status information of power grid can be perceived. In addition, the demand information of PEV owners should also be taken into account, so that the function of PEVs as transportation tools can be guaranteed. In this chapter, the possible scenarios of V2G implementation within both the household smart micro-grid and the smart regional grid will be discussed. The related mathematical formulation will also be analyzed. It is essentially an optimization problem, and the objective is to minimize the overall load variance of power grids. Case studies will be conducted. The results demonstrate that V2G operation can definitely help flatten the overall power load curves and it enables power grid to contain newly added PEV loads to some extent without boosting its capacity.