This paper applies the hosting-capacity method to a realistic distribution system. Under given circumstances the hosting capacity for Distributed Energy Resources (DER) identifies the degree of DER in power grid that can be accepted without endangering the reliability or quality of power. In this case study two limits setting the hosting capacity were evaluated: overvoltage and overcurrent. Finally it is examined to what extent the hosting capacity can be increased with use of real-time information and calculation of dynamic performance indications that govern the hosting capacity. It is shown that there is significant potential for increasing the hosting capacity without having to build new lines

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

Energy storage can potentially allow for more production from renewable resources into existing grids. A methodology to quantify grid limitations and dimension battery energy storage systems is presented in this paper. By use of grid consumption and production data, the hosting capacity methodology is developed as a general framework for storage dimensioning that can be applied by grid operators. The method is successfully applied to an existing subtransmission grid; actual hourly production and consumption data during a two-year period is used. The role of a storage system compared to other means to handle overloading is studied. It is found that about one third of overloading instances are suitable to handle with a battery energy storage system. After this, diminishing returns per unit of storage capacity are shown to occur.

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.

This paper presents the results of a feasibility study of a virtual power plant (VPP) in central Sweden designed to provide ancillary services to a 50-kV distribution network. The VPP consists of a wind park, hydro plant and reservoir as well as solar PVs and battery energy storage. The 50-kV subtransmission network was modeled in order to evaluate the ancillary services that could be provided by coordinating existing distributed energy resources in the network. Simulations were performed using measured hourly variations in production and consumption at all network nodes. The studied ancillary services include both reactive and active power control. Contribution from the VPP is evaluated for balancing, to enable a producer to meet spot markets bids and avoid purchases of balancing power minimize peak load in order to reduce subscribed power and tariff to the regional 130-kV network decrease network losses the contribution from reactive power control using the power converters to reduce the reactive power flow to the overlying network. Quantification of the economic gains from each operation case is provided.

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.

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.