  With the popularization of the electric vehicles (EVs), EV charging demand is
becoming an important load in the building. Considering the mobility of EVs
from building to building and their uncertain charging demand, it is of great
practical interest to control the EV charging process in a microgrid of
buildings to optimize the total operation cost while ensuring the transmission
safety between the microgrid and the main grid. We consider this important
problem in this paper and make the following contributions. First, we formulate
this problem as a Markov decision process to capture the uncertain supply and
EV charging demand in the microgrid of buildings. Besides reducing the total
operation cost of buildings, the model also considers the power exchange
limitation to ensure transmission safety. Second, this model is reformulated
under event-based optimization framework to alleviate the impact of large state
and action space. By appropriately defining the event and event-based action,
the EV charging process can be optimized by searching a randomized parametric
event-based control policy in the microgrid controller and implementing a
selecting-to-charging rule in each building controller. Third, a constrained
gradient-based policy optimzation method with adjusting mechanism is proposed
to iteratively find the optimal event-based control policy for EV charging
demand in each building. Numerical experiments considering a microgrid of three
buildings are conducted to analyze the structure and the performance of the
event-based control policy for EV charging.
