This paper presents the overvoltage caused by single and three-phase connected PV to a low-voltage distribution grid. Statistics are obtained based on source-impedance data for 40 000 customers. A stochastic approach is applied to a 28-customer low-voltage network and the probability of overvoltage is assessed. It is shown that the voltage rise due to single-phase connected PV is six times the rise for three-phase connected PV.To mitigate the overvoltage, grid-reinforcement, reactive power compensation, curtailment and coordinated connection of PV can be used. It is shown that reactive compensation is not effective in LV grids due to high R/X ratio. Coordinated connection helps in reducing the overvoltages caused by single-phase PV.Policy suggestions towards three-phase PV installations and coordinated single-phase PV connections are included in the paper.

This paper presents an IEC 61850 standard-based communication and aggregation solution for Demand-Response application, which allows end devices automatically detected, configured and integrated to the overlying Demand-Response system, thereby greatly increasing the integration efficiency, and making large scale of deployment feasible. This communication solution is dedicated to one community-wide Demand-Response application designed for a residential area near an industrial installation in Sweden. The community-wide Demand-Response application will be briefly explained in the paper, however, the main focus of this paper is the communication solution and IT system implementation for this application. The communication solution is realized by the unconventional use of IEC 61850 standard, and implemented in a hierarchical structure consisting of SCADA, communication gateway and low cost micro processor-based spatial heating controllers

This paper assesses the communication, information and functional requirements of Virtual Power Plants (VPPs). A conceptual formulation of the interoperability requirements is presented as well as a comparative study of their fulfillment by state-of-the-art communication techniques. VPP requirements are then mapped against services and information models of IEC 61850 and CIM power utility automation standards. Proposals are given for extensions of the IEC 61850 standard to enhance the interaction between VPP controller and the distributed energy resources. Finally the methodology and concepts are applied to a specific VPP consisting of hydro and wind plants, solar PV and storage facilities. Several applications to provide grid services from the proposed VPP in an existing 50 kV grid are covered. The implementation of the VPP communication and control architecture in the SCADA of demonstration plant is also presented.

The availability of monitoring, control and communication technology makes it possible to estimate the ampacity of an overhead transmission line continuously. This allows the transport of substantially larger amounts of energy over that line that when a static ampacity value is used. It is shown in this paper that the use of such dynamic line rating allows more wind power to be connected to the grid, i.e. it results in an increase of the hosting capacity. For the numerical example presented in the paper, the hosting capacity is increase from 214 to 390 MW. There are different types of risk associated with the introduction of dynamic line rating, some of which are discussed in this paper. Two main types of risk are distinguished. Risks associated with possible overload of components, even when the ampacity is exactly known. Additional risks due to the difference between the actual and the estimated ampacity.The introduction of curtailment, in combination with dynamic line rating, makes it possible to manage the first type of risk. The risk of overload carried by all customers is replaced by the risk of temporality being disconnected for the wind-park owner. The latter is however also the stakeholder gaining most from the increase in hosting capacity.To reduce the second type of risk, several practical aspects need to be considered before implementing dynamic line rating, several of which are discussed in this paper.

This paper summarizes the hosting capacity approach and gives some recent developments: including uncertainty in location and size of production units; curtailment to connect more production than according to the initial hosting capacity. For both developments it is shown that the transparency of the approach still holds but also that the results may be strongly location dependent. It is however also shown that the hosting-capacity approach can be used to obtain rough estimations, rules-of-thumbs, and to make a first assessment in case more detailed studies are not possible for example because insufficient data is available.

This paper describes the resonance introduced by adverse interaction of electronic converters. With the presence of multiple power-electronic converters, situations can occur where the harmonics are amplified due to the interaction between converters. An observation of undamped oscillation leading to instability in a microgrid is described. The term “converter induced resonances” is proposed to describe this phenomenon. The amount of distributed generation, active loads, FACTS and battery energy storage systems are expected to increase in future Smart Grids. All these resources will be interfaced with electronic converters. The potential impact of converter induced resonances in such grids is described. A coordinated design of the control systems of all converters is in practice not feasible. Each device will be independently tested to fulfil grid codes and have its own converter control implemented that can include functionality to modify voltage and /or current waveform.

This thesis develops methods to increase the amount of renewable energy sources that can be integrated into a power grid. The assessed methods include i) dynamic real-time assessment to enable the grid to be operated closer to its design limits; ii) energy storage and iii) coordinated control of distributed production units. Power grids using such novel techniques are referred to as “Smart Grids”. Under favourable conditions the use of these techniques is an alternative to traditional grid planning like replacement of transformers or construction of a new power line. Distributed Energy Resources like wind and solar power will impact the performance of the grid and this sets a limit to the amount of such renewables that can be integrated. The work develops the hosting capacity concept as an objective metric to quantify the ability of a power grid to integrate new production. Several case studies are presented using actual hourly production and consumption data. It is shown how the different variability of renewables and consumption affect the hosting capacity. The hosting capacity method is extended to the application of storage and curtailment. The goal is to create greater comparability and transparency, thereby improving the factual base of discussions between grid operators, electricity producers and other stakeholders on the amount and type of production that can be connected to a grid.Energy storage allows the consumption and production of electricity to be decoupled. This in turn allows electricity to be produced as the wind blows and the sun shines while consumed when required. Yet storage is expensive and the research defines when storage offers unique benefits not possible to achieve by other means. Focus is on comparison of storage to conventional and novel methods.As the number of distributed energy resources increase, their electronic converters need to provide services that help to keep the grid operating within its design criteria. The use of functionality from IEC Smart Grid standards, mainly IEC 61850, to coordinate the control and operation of these resources is demonstrated in a Research, Development and Demonstration site. The site contains wind, solar power, and battery storage together with the communication and control equipment expected in the future grids.Together storage, new communication schemes and grid control strategies allow for increased amounts of renewables into existing power grids, without unacceptable effects on users and grid performance.

Avhandlingen studerar hur existerande elnät kan ta emot mer produktion från förnyelsebara energikällor som vindkraft och solenergi. En metodik utvecklas för att objektivt kvantifiera mängden ny produktion som kan tas emot av ett nät. I flera fallstudier på verkliga nät utvärderas potentiella vinster med energilager, realtids gränser för nätets överföringsförmåga, och koordinerad kontroll av småskaliga energiresurser. De föreslagna lösningarna för lagring och kommunikation har verifierats experimentellt i en forskning, utveckling och demonstrationsanläggning i Ludvika.

This paper presents the use of curtailment to allow more wind or solar power to be connected to a distribution network when overcurrent or overvoltage set a limit. Four case studies, all based on measurements, are presented. In all cases the hosting capacity method is used to quantify the gain in produced energy for increased levels of distributed renewable energy resources. A distinction is made between “hard curtailment” where all production is disconnected when overcurrent and overvoltage limits are exceeded and “soft curtailment” where the amount of production to be disconnected is minimized. It is shown that the type of curtailment method used has a large impact on the amount of delivered energy to the grid. The paper further discusses details of the curtailment algorithm, alternatives to curtailment, the communication needs and risks associated with the use of curtailment

This paper defines a step-by-step systematic decision making process to define operant conditions and applications for which battery storage is an option for electrical power grids. The set of rules is based on a number of research studies performed by the authors focusing mainly on sub-transmission grids. Battery storage is expensive so the focus in this paper is on comparing storage with other ways of achieving the same increase in the hosting capacity (HC) of grid. The approach is to find niche applications for which battery storage has unique advantages i.e. it provides a unique alternative for grid operator planning, which is unachievable in other ways. The first step is to assess the grid’s capacity to host new loads or production. This constitutes a baseline for evaluation of improvements from storage. The next step is to define applications for battery energy storage. Integrating new loads/production without increasing the hosting capacity may result in reduced performance and ultimately loss of production or consumption. The cost and severity of exceeding the hosting capacity will also affect the type of solution required. After this define the conventional planning solutions that would be adopted without storage option available. Such measures may include upgrading of transformer or construction of new power line. Curtailment, tariff based incentives or contracted load shedding as well as techniques like dynamic line rating can also be included in the comparison at this stage. Based on assessments of these alternatives it is possible to compare increase in hosting capacity with and without storage as well as comparing gains with storage to what can be achieved with conventional grid planning options or other novel methods. It is also important to investigate the regulatory framework and constraints regarding ownership and operation of a battery energy storage. Should the grid operator own the battery storage? Or should the task be outsourced on a service contract or the service purchased in the market place? Storage capacity may only be utilized during certain periods. Can all or part of the storage capacity or the power electronic inverters perform additional functions and increase the return on investment for the installation? Regulatory aspects regarding the possibilities for different actors to pursue such additional income streams should be included in the assessment to correctly determine the return of investment of battery storage.The final step should include control algorithm development, tested in a flexible but realistic environment and should establish whether the system actually delivers the predicted outcomes when exposed to real-time data. This may require building a pilot installation as a research and development activity before commercial deployment.