Chresten Traholt

Average behavior of battery-electric vehicles for distributed energy studies

The increased focus on electric vehicles (EVs) as distributed energy resources calls for new concepts of aggregated models of batteries. Despite the developed battery models for EV applications, when looking at the scenarios of energy storage, both geographical-temporal aspects and EVs use conditions cannot be neglected for an estimation of the available fleet energy. In this paper we obtained an average behavior of battery-EVs, in relation to a number of variables such as current rates for charging and discharging, temperature, depth-of-discharge and number of cycles. An average approach was applied to calculate the influence of each variable on the battery energy and lifetime. The obtained results show that battery-EVs are nonlinear time-variant systems which however can be modeled with good approximation if time, geographical location and battery use conditions are known.

Analysis of voltage support by electric vehicles and photovoltaic in a real Danish low voltage network

With conventional generating units being replaced by renewable sources which are not required to provide same high level of ancillary services, there is an increasing need for additional resources to achieve certain standards regarding frequency and voltage. This paper investigates the potential of incorporating electric vehicles (EVs) in a low voltage distribution network with high penetration of photovoltaic installations (PVs), and focuses on analysing potential voltage support functions from EVs and PVs. In addition, the paper evaluates the benefits that reactive power control may provide with addressing the issues regarding voltage control at the expense of increased loading. Analysed real Danish low voltage network has been modelled in Matlab SimPowerSystems and is based on consumption and PV production data measured individually for number of households.

Implementation and demonstration of grid frequency support by V2G enabled electric vehicle

Safe operation of the electric power system relies on conventional power stations. In addition to providing electrical energy to the network, some power stations also provide a number of ancillary services for the grid stability. These services could potentially be provided by the growing number of electric vehicles - faster and with better precision, using Vehicle-to-Grid technology. This paper explores the implementation of a system that demonstrates the use of the electric vehicles for providing frequency regulation in the Danish power grid. The system is tested with the use case of Primary Frequency Regulation. The service is implemented following the technical conditions for ancillary services in the Danish grid. The real life system is developed using Web-centric communication technologies between the components. Communication and control functions of the system are validated through experiments. The response of the system is studied in terms of latency, precision and stability.

Planning future electric vehicle central charging stations connected to low-voltage distribution networks

A great interest is recently paid to Electric Vehicles (EV) and their integration into electricity grids. EV can potentially play an important role in power system operation, however, the EV charging infrastructures have been only partly defined, considering them as limited to individual charging points, randomly distributed into the networks. This paper addresses the planning of public central charging stations (CCS) that can be integrated in low-voltage (LV) networks for EV parallel charging. The concepts of AC and DC architectures of CCS are proposed and a comparison is given on their investment cost. Investigation on location and size of CCS is conducted, analyzing two LV grids of different capacity. The results enlighten that a public CCS should be preferably located in the range of 100 m from the transformer. The AC charging levels of 11 kW and 22 kW have the highest potential in LV grids. The option of DC fast-charging is only possible in the larger capacity grids, withstanding the parallel charge of one or two vehicles.

High temperature superconductor machine prototype

A versatile testing platform for a High Temperature Superconductor (HTS) machine has been constructed. The stationary HTS field winding can carry up to 10 coils and it is operated at a temperature of 77K. The rotating armature is at room temperature. Test results and performance for the HTS field winding comprising four coils wound with two types of HTS tapes are shown and discussed. The field winding produces up to 0.62T in the 10mm air gap which constitutes 78% of the armature design value. Recommendations for the field winding operation are proposed and verified, which resulted in an increase of available magneto-motive force of the field winding up to 25%.

Power quality issues into a Danish low-voltage grid with electric vehicles

An increased interest on electric vehicles (EVs) and plug-in hybrid electric vehicles (PHEVs) is dealing with their introduction into low voltage (LV) distribution grids. Lately, analysis on power quality issues has received attention when considering EVs as additional load. The charging of EVs is expected without a centralized coordination in the first years, therefore a study on voltage variations and loading of LV grids is needed to estimate the immediate impact by EVs. In this work, the modeling and simulation of a Danish residential LV grid is conducted considering the two scenarios of dumb charging and overnight charging. The effect of different shares of EVs on voltage variations and transformer loading is assessed and analyzed. Results have shown that if single-phase, 16 A charging is employed, the actual LV grid would withstand the contingency of up to 30–40% of EVs charging overnight.

A dynamic behaviour analysis on the frequency control capability of electric vehicles

The paper presents results of a study on the dynamic response of Electric Vehicles (EV) when participating in frequency control of an islanded system. The following cases were considered: when there is no EV performing frequency control, when the EV participates in primary frequency control and when the EV participates in both primary and secondary frequency control. Different parameters are tested in various combinations, and their influence on frequency deviation as well as power and energy provided by the EV with vehicle-to-grid (V2G) capability is shown.

A study on electricity export capability of the μCHP system with spot price

When a number of μCHP systems are aggregated as a Virtual Power Plant (VPP), they will be able to participate in the electricity wholesale market with no discrimination compared to conventional large power plants. Hence, this paper investigates the electricity export capability of the μCHP system when the electricity buyback price is given at a value equalizing the dynamic spot price. A μCHP system is modeled with optimized generation, and the marginal price of electricity export for such system is explained. A sensitivity analysis of several key factors, e.g. fuel price, heat to power ratio of the μCHP unit, which influence the export capability of μCHP system, is firstly carried out in the intraday case study, followed by the annual case study which explores the annual system performance. The results show that the electricity export capability of a μCHP system is closely related to its technical parameters, the associated energy price during the trade, as well as the demand profile. Furthermore, the μCHP system running under fluctuating spot price is likely to gain more profit than that running under a fixed electricity export price.

Cost-benefit analysis of a novel DC fast-charging station with a local battery storage for EVs

The increasing penetration of Electric Vehicles (EVs) and their charging systems is representing new high-power consumption loads for the distribution system operators (DSOs). To solve the problem of the EV range in terms of driving kilometers, the car manufacturers have invested resources on new EV models by increasing the size of the batteries. To satisfy EV load demand of the new EV models in urban areas the public DC Fast-Charging Station (DCFCS) is indispensable to recharge EVs rapidly. The introduction of the Battery Energy Storage within the DCFCSs is considered in this paper an alternative solution to reduce the operational costs of the charging stations as well as the ability to mitigate negative impacts during the congestion on the power grids. An accurate description of the DCFCS and its design system has been implemented, which is able to decouple the peak load demand caused by EVs on the main grid and decrease the connection fees. Finally, an economic evaluation is done to evaluate the feasibility and the cost-benefit analysis (CBA) of the DCFCSs. The proposed approach considers various technical and economic issues, such as cost of installation, connection fees and life cycle cost of the batteries. The proposed cost-benefit analysis can be used to verify the effectiveness and applicability of DCFCS in large scale.

Energylab Nordhavn: An integrated community energy system towards green heating and e-mobility

This paper analyzes the green potential of a newly developed urban community, i.e., Nordhavn, in Copenhagen, Denmark from a planning perspective, wherein the energy sector of power, heat and transportation will be developed as an integrated energy system solution. Based on an hour-by-hour analysis wherein the generation and demand in each energy sector are balanced, the analysis explains how different levels of penetration of centralized heat pumps (HPs) and electric vehicles (EVs) would influence the energy performance of this integrated community energy system. The performance of the integrated energy system is evaluated from the perspectives of annual fuel consumption, electricity import, system cost and CO2 emission, etc.