  This paper presents a predictive controller for handling plug-and-play (P&P)
charging requests of flexible loads in a distribution system. We define two
types of flexible loads: (i) deferrable loads that have a fixed power profile
but can be deferred in time and (ii) shapeable loads that have flexible power
profiles but fixed energy requests, such as Plug-in Electric Vehicles (PEVs).
The proposed method uses a hierarchical control scheme based on a model
predictive control (MPC) formulation for minimizing the global system cost. The
first stage computes a reachable reference that trades off deviation from the
nominal voltage with the required generation control. The second stage uses a
price-based objective to aggregate flexible loads and provide load shaping
services, while satisfying system constraints and users' preferences at all
times. It is shown that the proposed controller is recursively feasible under
specific conditions, i.e. the flexible load demands are satisfied and bus
voltages remain within the desired limits. Finally, the proposed scheme is
illustrated on a 55 bus radial distribution network.
