• Energy Research

In a context of extensive electrification of the transport sector, the use of flexibility services from electric vehicles (EVs) is becoming of paramount importance. This paper defines a market framework for enabling EVs flexibility at the distribution level, considering grid constraints. The main objective is to establish an adequate incentive system and proceed with an evaluation of EVs grid support for both users and DSOs, benchmarking it against the typical reinforcement solution. To exploit this framework, a billing process based on a two-price system is proposed for the controlled EV charging. The derived methodology is applied to a piece of semi-urban Danish distribution grid consisting of 42 customers. The service remuneration spans from 16 \text{C}\!\!\!\!\!\!\! {=}/year to 51 \text{C}\!\!\!\!\!\!\! {=} (year per customer, depending on the incentive scheme, and avoids a standard reinforcement of approximately 6200 \text{C}\!\!\!\!\!\!\! {=}/year. It is demonstrated the benefit for DSOs and society, proving a technical and economic feasible solution.

The paper characterizes dynamics and modelling of a Lithium-ion battery. Theoretical formulation and literature review are combined to derive the necessary battery characterization. The three main dynamics for modeling the battery are: direct-current electrical equivalent circuit, state-of-charge (SOC) and thermal dynamic. Furthermore, the capacity fade caused by degradation is considered as a fourth dynamic. Degradation is considered as the sum of calendar aging and cycling loss dynamics. The modeling procedure has general validity and can be used for different battery chemistries by changing specific parameters. The model is tailored for a 40 kWh Lithium Nickel Manganese Cobalt (NMC) Oxide battery, which is currently used in the Nissan LEAF 2018. Considering a user driving 45 km/day and the temperature of the years 2017 and 2018 in Denmark, the battery capacity fade is found to be between 2 and 5% of the battery capacity after two years of use. Degradation is highly dependent on the average level of SOC during the years.

Abstract Electricity and transport sectors have to be decarbonised in order to mitigate climate change effects leading to increased penetration of distributed energy systems (DES) and electric vehicles (EV) which can threaten the security of distribution grid operation. Proper design and operation of such systems are crucial if the adverse effects on the grid are to be avoided. Moreover, EVs represent a high load and should not be considered merely as passive assets since they can provide various flexibility services for maintaining the grid stable. This paper presents a multi-domain optimisation framework for minimising carbon emission in low-voltage distribution grids with high share of distributed energy resources and electric vehicles. The framework determines optimal EV flexibility usage (both active and reactive) while satisfying electric and thermal building demands, and maintaining the distribution grid in the stable operation. The model was applied to a real low-voltage Danish distribution grid where measurement data is available on hourly basis in order to determine EV flexibility impacts on carbon emissions, as well as the benefits of optimal DES design. The influence of EV reactive power control on the grid operation, in addition to coordinated charging, is analysed. Results showed that when the system can be optimally designed, emissions decrease by 64% and additionally 32% with proactive EV integration, whereas EV reactive power control enables integration of larger EV amounts and provides significant voltage support without affecting the user comfort.

This paper introduces a novel design of an electric vehicle (EV) fast charging station, consisting of a battery energy storage system (BESS) with reconfigurable cell topology. The BESS comprises two battery strings that decouple the power flow between EV and grid, to enable charging powers above the grid capacity. The reconfigurable design is achieved by equipping the battery cells with semiconductor switches and serves two main purposes. First, it aims at solving cell unbalance issues to increase safety, reliability, and lifetime of the battery. Second, it enables the BESS to actively control the EV charging process by changing its cell configuration in a real-time fashion, making a DC-DC converter redundant. The paper presents a modelling approach that captures the reconfigurable design including the controlling algorithm used for cell engagement. The simulation results show that the BESS is able to fulfil the EV request with sufficient accuracy for most of the fast charging process. However, the switching of cells leads to variations in the charging current that can potentially exceed the tolerance band defined in IEC61851-23. Therefore, complementary measures are suggested to achieve a suitable current control during all phases of the charging process. The estimated BESS efficiency during the EV fast charging process is 93.3%. The losses caused by the reconfigurable design amount to 1.2% of the provided energy. It is demonstrated that the proposed design has a competitive efficiency compared to a battery buffered fast charging station with DC-DC converter.

This paper outlines an overview of the general requirements for the control rooms of the future power systems (2030+). The roles and activities in the future control centres will evolve with respect to the switching, dispatching and restoration functions currently active. The control centre operators will supervise on the power system and intervene - when necessary - thanks to the maturation and wide scale deployment of flexible controls. For the identification of control room requirements, general trends in power system evolution are considered and mainly the outcomes of the ELECTRA IRP project, that proposes a new Web-of-Cell (WoC) power system control architecture. Dedicated visualization features are proposed, aimed to support the control room operators activities in a WoC oriented approach. Furthermore, the work takes into account the point of view of network operators about future control rooms and feedback about the proposed visualization features, collected by means of interviews and questionnaires.

The Danish government has set very ambitious binding targets regarding decarbonization. By 2030, carbon dioxide emissions must be reduced by 70% compared to the 1990 level. This can be achieved primarily through a predominantly renewables-based electricity system and the electrification of energy demand.

Summary form only given. The paper proposes the modeling and the optimal management of a hot-temperature (Sodium Nickel Chloride) battery system coupled with wind generators connected to a medium voltage grid. A discrete-time model of the storage device reproducing the battery main dynamics (i.e., state of charge, temperature, current, protection, and limitation systems) has been developed. The model has been validated through some experimental tests. An optimal management strategy has been implemented based on a forward dynamic programming algorithm, specifically developed to exploit the energy price arbitrage along the optimization time horizon (“generation shifting”). Taking advantage of this strategy wind generation performances can be enhanced and adapted to load demand, obtaining an increased economic gain measured by the difference between the economic revenue obtained with and without the proposed generation shifting policy.