The integration of plug-in electric vehicles (PEVs) to power systems has impacts on the stability characteristics of the integrated systems. Wide area controllers (WACs) are used in power systems to provide auxiliary control signals to the generators or other devices in order to improve the stability of the system. The necessity of WACs becomes more relevant during grid-to-vehicle (G2V) or vehicle-to-grid (V2G) power transactions, that is, charging and discharging cycles of the PEVs respectively. The design of a WAC for providing damping to three generators in a 12-bus power system with PEVs is presented in this study. Each WAC signal is obtained based on the aggregation of modulated local and remote power system stabilisers' signals. The modulation indices associated with those signals are tuned using the particle swarm optimisation technique to provide the maximum damping to the three generators. The 12-bus power system with the PEVs and WAC has been implemented on the real-time digital simulator (RTDS). Typical results have been presented to show the improvement in the stability of the power system when PEVs are integrated using transient simulations and Prony analysis.