Chresten Træholt

A Decentralized Storage Strategy for Residential Feeders With Photovoltaics

This paper proposes a decentralized storage strategy to support voltage control in low-voltage (LV) residential feeders with high photovoltaic (PV) capacity installed. The proposed strategy is capable of preventing overvoltage situations during high PV generation periods, by the use of locally controlled battery energy storage systems (ESS) at the PV system grid interface. The traditional way of operating a domestic ESS is based on charging the battery as soon as the PV generation exceeds the consumption, without taking into account overvoltage events during high PV generation hours; the proposed storage concept improves the traditional approach, thanks to the provision of voltage support. A novel method, based on voltage sensitivity analysis, identifies a common power threshold that triggers the ESSs activation in the feeder. A Belgian residential LV feeder is used as a case study. Time-series simulations based on 1-year load and generation profiles verify the method findings and quantify the ESS size in terms of storage power and energy level.

Loss and inductance investigations in a 4-layer superconducting prototype cable conductor

One important issue in the design and optimization of a superconducting cable conductor is the control of the current distribution between single tapes and layers. This presentation is based on a number of experiments performed on a 4-layer three meter long prototype superconducting cable conductor. The self and mutual inductances of the layers are studied theoretically. The current distribution between the superconducting layers is monitored as a function of transport current. The results are compared with the expected current distribution given by the authors equivalent electrical circuit model. The AC losses are measured as a function of transport current and a given current distribution and compared with the monoblock model. Recommendations for design of future cable conductor prototypes are given.

Driving Pattern Analysis for Electric Vehicle (EV) Grid Integration Study

In order to facilitate the integration of electric vehicles (EVs) into the Danish power system, the driving data in Denmark were analyzed to extract the information of driving distances and driving time periods which were used to represent the driving requirements and the EV unavailability. The Danish National Transport Survey data (TU data) were used to implement the driving data analysis. The average, minimum and maximum driving distances were obtained for weekdays, weekends and holidays to illustrate the EV users¿ driving requirements in different days. The EV availability data were obtained from the driving time periods to show how many cars are available for charging and discharging in each time period. The obtained EV availability data are in one hour time periods and one quarter time periods for different study purposes. The EV availability data of one hour time period are to be used for optimal EV charging study in energy power market. The EV availability data of quarter time periods are to be used to investigate the possibility of utilizing EVs for providing regulation power. The statistical analysis software, SAS, was used to carry out the driving data analysis.

Design Study of 10 kW Superconducting Generator for Wind Turbine Applications

We have performed a design study of a 10 kW superconducting slow rotating generator suitable for demonstration in a small scale wind turbine, where the drive train only consists of the turbine blades connected directly to the generator. The flux density in the superconducting rotor is chosen as B = 1 Tesla to be similar to the performance of permanent magnets and to represent a layout, which can be scaled up in future off-shore wind turbines. The proposed generator is a 8 pole synchronous machine based on race-track coils of high temperature superconducting tapes and an air cored copper stator enclosed in an iron shield.

EV Charging Facilities and Their Application in LV Feeders With Photovoltaics

Low-voltage (LV) grid feeders with high penetration of photovoltaics (PVs) are often affected by voltage magnitude problems. To solve such issues, previous research has shown that reactive power methods, active power curtailment and grid reinforcement can be used for voltage support, yet showing several limits. We introduce the use of electric vehicle (EV) public charging stations with energy storage system (ESS) as a solution for voltage regulation in LV feeders with PV. A novel method is proposed to determine the ESS charging load required for voltage regulation and compare the results for the different locations in the feeder. With time-series simulations, we quantify the energy size required for a station ESS. A Belgian LV residential grid, modeled using real PV generation and load profiles, is used as case study. The method and simulation results show the effectiveness of using public EV charging facilities with the additional function of voltage regulation in feeders with PV.

Evaluation of a Generic Virtual Power Plant framework using service oriented architecture

The purpose of this paper is to find and describe a suitable software framework that can be used to help implement the concept of a generic virtual power plant in the future power system. The generic virtual power plant concept, along with the utilization of distributed energy resources, has many interesting properties that can influence the future shape of power markets. The concept holds many promises including cheaper power to the consumer, a more flexible and responsive power production and the support of a more environment- friendly development. In order to realize a software solution supporting the generic virtual power plant, an array of different software design principles, patterns and architectures must be applied. Especially Service Oriented Architecture (SOA) can aid in implementing the generic virtual power plant. An analysis of the Nordic power market has been carried out in order to identify potential issues and barriers, henceforth mentioned as challenges, connected with the introduction of the generic virtual power plant concept. In this paper, three use case scenarios will show how each of these challenges can be overcome by the proposed solution framework. The use case scenarios will be tested by a prototype that has been developed as proof of concept.

Towards Faster FEM Simulation of Thin Film Superconductors: A Multiscale Approach

This work presents a method to simulate the electromagnetic properties of superconductors with high aspect ratio such as the commercially available second generation superconducting YBCO tapes. The method is based on a multiscale representation for both thickness and width of the superconducting domains. A couple of test cases were successfully simulated and further investigations were made by means of structured (mapped) meshes. Here, large aspect ratio elements were used to simulate thin material layers with a reduced number of elements. Hence, more complex geometries can be studied at considerable lower computational time. Several test cases were simulated including transport current, externally applied magnetic field and a combination of both. The results are in good agreement with recently published numerical simulations. The computational time to solve the present multiscale approach in 2D is estimated as two orders of magnitude faster than other 2D methods.

Facilitating a Generic Communication Interface to Distributed Energy Resources: Mapping IEC 61850 to RESTful Services

As the power system evolves into a smarter and more flexible state, so must the communication technologies that support it. A key requirement for facilitating the distributed production of future grids is that communication and information are standardized to ensure interoperability. The IEC 61850 standard, which was originally aimed at substation automation, has been expanded to cover the monitoring and control of Distributed Energy Resources (DERs). By having a consistent and well- defined data model the standard enables a DER aggregator, such as a Virtual Power Plant (VPP), in communicating with a broad array of DERs. If the data model of IEC 61850 is combined with a set of contemporary web protocols, it can result in a major shift in how DERs can be accessed and coordinated. This paper describes how IEC 61850 can benefit from the REpresentational State Transfer (REST) service concept and how a server using these technologies can be used to interface with DERs as diverse as Electric Vehicles (EVs) and micro Combined Heat and Power (µCHP) units.

Improvement of Local Voltage in Feeders With Photovoltaic Using Electric Vehicles

In low-voltage (LV) feeders with high penetration of photovoltaic (PV), a major issue to be solved is voltage rise due to the active power injection. If no measures are taken, this may lead to generations interruptions and to the malfunctioning of domestic appliances due to non-standard voltage profiles. This paper proposes a storage strategy to alleviate voltage rise in feeders with PV, using coordinated electric vehicle (EV) load as the storage solution. The voltage support strategy is easy to implement practically and it is demonstrated on a test feeder emulating a household with roof-mounted PV and an EV. The results show the effectiveness of using coordinated EV load in feeders with PV to mitigate voltage rise problems.

Integration of Fuel Cell Micro-CHPS on Low Voltage Grid: A Danish Case Study

The future significance of fuel cell (FC) powered micro combined heat and power (micro-CHP) units in meeting the residential energy demands is set to increase, which may have a considerable impact on the low voltage (LV) grid. The objective of this paper is to investigate into the related technical issues using a Danish case study with different penetration levels of uncoordinated FC micro-CHPs. Based on the findings, it is recommended to design grid oriented integration strategies such as Virtual Power Plants (VPPs) for achieving future smart grids with a large roll out of distributed energy resources (DER).