  Electric Vehicles (EVs), as their penetration increases, are not only
challenging the sustainability of the power grid, but also stimulating and
promoting its upgrading. Indeed, EVs can actively reinforce the development of
the Smart Grid if their charging processes are properly coordinated through
two-way communications, possibly benefiting all types of actors.
  Because grid systems involve a large number of actors with nonaligned
objectives, we focus on the economic and incentive aspects, where each actor
behaves in its own interest. We indeed believe that the market structure will
directly impact the actors' behaviors, and as a result the total benefits that
the presence of EVs can earn the society, hence the need for a careful design.
This survey provides an overview of economic models considering unidirectional
energy flows, but also bidirectional energy flows, i.e., with EVs temporarily
providing energy to the grid. We describe and compare the main approaches,
summarize the requirements on the supporting communication systems, and propose
a classification to highlight the most important results and lacks.
