Comparison of control strategies for electric vehicles on a low voltage level electrical distribution grid

Abstract

If electrical energy demand is not balanced with electricity generation the results are additional electrical power grid investments and system stability risks. An increasing energy demand caused by charging plug-in electric vehicles (PEVs) is expected to affect distribution grid levels in the future. Uncontrolled PEV charging causes additional grid stress but PEVs are also capable of balancing the demand to the present supply situation via charging control strategies. Different control strategies for PEVs have been tested to address this issue. They can be classified as indirect, direct and autonomous control strategies. However, it is still under discussion, which charging strategy is best suited to integrate PEVs into feature dependent power generation on a distribution grid level. We investigated the advantages and weaknesses of autonomous control via local voltage measurement compared to direct and indirect charging control. Here we found that autonomous control of PEVs can counteract voltage dips caused by simultaneous charging. This is of great benefit for smart grids because autonomous control realised with PEVs internal systems can reduce the investment in communication technology on the infrastructure side. Nevertheless, this research also shows the limits of autonomous control. It can be concluded that a mix of different control strategies is necessary to realise PEVs demand response opportunities. Autonomous control will play an important role supporting the control of PEVs to stabilise smart grids.