  Plug-in electric vehicles (PEVs) can serve in discharge mode as distributed
energy and power resources operating as vehicle-to-grid (V2G) devices and in
charge mode as loads or grid-to-vehicle (G2V) devices. It has been documented
that PEVs serving as V2G systems can offer possible backup for renewable power
sources, can provide reactive power support, active power regulation, load
balancing, peak load shaving,% and current harmonic filtering, can provide
ancillary services as frequency control and spinning reserves, can improve grid
efficiency, stability, reliability, and generation dispatch, can reduce utility
operating costs and can generate revenue. Here we show that PEVs can even
improve power grid transient stability, that is, stability when the power grid
is subjected to large disturbances, including bus faults, generator and branch
tripping, and sudden large load changes. A control strategy that regulates the
power output of a fleet of PEVs based on the speed of generator turbines is
proposed and tested on the New England 10-unit 39-bus power system. By
regulating the power output of the PEVs we show that (1) speed and voltage
fluctuations resulting from large disturbances can be significantly reduced up
to 5 times, and (2) the critical clearing time can be extended by 20-40%.
Overall, the PEVs control strategy makes the power grid more robust.
