Abstract
As a consequence of the exponential growth of the electric vehicle (EV) market, DC fast-charging infrastructure is being rapidly deployed all around the world. Ultra-fast charging (UFC) stations are starting to pose serious challenges to the electric power system operation, mostly due to their high peak power demand and unregulated discontinuous operation. To address these issues, local energy storage can be installed, ensuring a smoother grid power absorption profile and allowing to provide grid-supporting features. In this work, a control solution for the grid-side AC/DC converter of next-generation EV UFC stations is proposed. A virtual synchronous compensator (VSC) control algorithm is implemented, in order to lessen the impact of the charging station on the utility and to provide the full spectrum of grid ancillary services (i.e., frequency regulation, reactive power compensation, harmonic reduction, short circuit current generation, etc.). The proposed control strategy is verified experimentally on a downscaled 15 kVA three-phase inverter, emulating the grid front-end of the charging station.
Highlights
Despite the constantly increasing performance and energy density of Li-ion batteries, their cost and weight still poses a major limit to electric vehicle (EV) driving range [1]
It must be noted that the participation to primary frequency control is usually an optional feature and in the case of Ultra-fast charging (UFC) it could represent an additional stream of revenues after proper agreements with the grid operator
It can be concluded that the proposed S-virtual synchronous compensator (VSC) control strategy applied to the active front-end (AFE) of a bidirectional UFC station outperforms traditional D-STATCOMs, being able to condense in a single controller all of the relevant grid ancillary services
Summary
Despite the constantly increasing performance and energy density of Li-ion batteries, their cost and weight still poses a major limit to electric vehicle (EV) driving range [1]. The availability of stored energy opens up the possibility of providing grid ancillary services, such as (1) active power injection/absorption for grid frequency regulation, (2) reactive power support for voltage regulation, (3) grid harmonic reduction and (4) fault current generation during voltage dips/swells These features can directly support the power distribution system, effectively turning around the drawbacks of conventional UFC stations, allowing for an additional revenue stream for the station operator [16]. The advantage of this technology is that the inverter can mimic one or more aspects of a real SG, contributing to the correct operation of the electric grid Even though this solution has been mainly proposed for generating units (such as solar fields), it can be applied to UFCs in order to make them more grid friendly, by providing ancillary services exploiting the already available power hardware.
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