This paper investigates electric vehicle (EV) participation in the flexible ramp market. We take into account EV stochastic mobility, and evaluate impact on power system reliability and flexibility. Based on dynamic programming, the model deals with uncertainties and variations of net load, as well as EV charging requirements. Markov process is utilized in estimating the aggregated power capacity of EVs. Two participation modes are analyzed: 1) EV direct provision of the ramp product; and 2) EV cooperation with the conventional generator. Moreover, we propose new indices to evaluate power system flexibility. Finally, numerical experiments are conducted to validate the proposed approach and illustrate how EV involvement into the ramp market can improve power system reliability and flexibility.Index Terms-Electric vehicles (EVs), flexibility, ramp market, reliability.
NOMENCLATURE λVehicles' arrival rate into the traffic system. μ Reciprocal of the mean travel time. m Maximum capacity of the traffic system. γ ij Transition rate from states i to j of the Markov model. E sij+ Discharging energy per electric vehicle (EV) under states i or j. ω sij+ Mean discharging energy per EV under states i or j. σ sij+ Standard deviation of the discharging energy per EV under states i or j. F Z+ (z) Cumulative distribution of EV available discharging energy. f Z+ (z) Probability density function of EV aggregated discharging energy. C EVtotal EV total battery capacity in one large area. q Average energy per EV to finish the travel. Energy + EV aggregated energy capacity for discharging. Energy − EV aggregated energy capacity for charging. h Time duration of EV charging/discharging. Power + EV aggregated discharging power. r + max Maximum discharging rate for one EV. p max EV+ EV aggregated discharging power capacity. p EVG+ EV discharging power in the market. p EVG− EV charging power in the market. FRU EV EV ramp up service in the market. FRD EV EV ramp down service in the market. G Set of the on-line generators. p t Gi Generation output of generator i at time t. FRU t i Ramp up service of generator i at time t. FRD t i Ramp down service of generator i at time t. C FRUi Cost of the ramp up service for generator i. C FRDi Cost of the ramp down service for generator i. C EVG Cost for EVs to provide the energy service. C EVFRU Cost for EVs to provide the ramp up service. C EVFRD Cost for EVs to provide the ramp down service. P t L Net load at time t. p t EVG− EV charging load at time interval t. p min Gi Minimum generation of the generator i. p max Gi Maximum generation of the generator i. R i Ramp rate of the generator i. t Time interval period to ramp up or down. D t FRU System requirement for ramping up at time t. D t FRD System requirement for ramping down at time t. E t EV EV aggregated energy at time t. η + EV discharging coefficient. η − EV charging coefficient. C req EV energy requirement.