Potentials of Electric Vehicles for the Provision of Active and Reactive Power Flexibilities as Ancillary Services at Vertical Power System Interconnections

TL;DR

This paper assesses the active and reactive power flexibility of electric vehicles within European medium voltage systems, considering regulatory constraints and bidirectional charging, to evaluate their potential as ancillary services and inform grid planning.

Contribution

It introduces a method to determine the feasible operation region of EVs' power flexibility under regulatory guidelines and evaluates their impact on system flexibility and constraints.

Findings

Flexibility polygon derived for EV bidirectional charging.

System flexibility potential varies with EV penetration levels.

Cost curve for EV active power flexibility introduced.

Abstract

This paper extends the research regarding the determination of the feasible operation region under the impact of electric vehicles. Thereby, the active and reactive power flexibility potentials of EV for alternating current and direct current bidirectional charging are limited in first instance by regulatory guidelines. In this paper German regulatory guidelines are applied to depicture the current state of the art for EV charging components. Under assumption of bidirectional charging for EV, the corresponding flexibility polygon in the PQ plane is derived. The impact on the FOR is then evaluated within the Cigr\'e European medium voltage benchmark system. In a first step, the flexibility potential of the system is determined for a load case as basis for the comparison with different, realistic penetration levels of EV. DER are considered to depict additional existing power flexibilities. In a second step, the FOR and the corresponding limitations within the system are analyzed. Under variation of the rated line current, the limiting utility constraints are pointed out. The obtained results are the basis for more detailed investigations regarding the potentials of bidirectional charging for an intensified system operators cooperation. The used method presents a promising approach to be used by the lower system operator as tool in the grid planning process to estimate the possible power flexibilities that can be provided to a higher system. Continuing, the potential for ancillary services provided by EV is discussed, resulting in the derivation of future research aspects. Because the accumulation of EV leads to higher grid utilization, which results in quadratically increasing grid losses the closer the grid is operating to the grid constraints, a cost curve for the EVs active power flexibility is introduced, whereas probability zones are indicated.