Real-time plug-in electric vehicle charging strategies for current and voltage unbalance minimization

Plug-in electric vehicles (PEVs) have been proposed as one of the solutions to reduce transportation dependency on oil. Nevertheless, if PEVs are introduced as a new load on the grid without any charging strategy, the grid's power quality will be deteriorated. Among the power quality parameters, current and voltage unbalances would be affected. This paper proposes a real-time strategy in order to minimize the current unbalance factor (CUF) caused by PEVs and housing on a common connection point (CCP) in a residential network. As a consequence of the CUF minimization, the voltage unbalance factor (VUF) is significantly reduced. The CUF at a CCP is formulated as a function of the loads in-phase and quadrature currents (PEVs and householders included). This objective function is minimized under maximum rating and charging priority constraints using algorithm Active-set. The minimization process is a part of the strategy which consists in adapting the optimization problem in real-time to changing conditions such as PEV's arrival and departure times, PEV's battery capacity variety, a random initial state-of-charge (SOC) and the householder's consumption. The strategy was tested on a low voltage network simulated on Matlab /Simulink. Results show that the current balance index is increased more than 400%, the voltage unbalance index is reduced 17% and some of the CCPs in the electric network simulated, are re-balanced (based on the EN50160 standard's definition) thanks to the CUF minimization.