Analytical Approach for Active Distribution Network Restoration Including Optimal Voltage Regulation

The ever increasing utilization of sensitive loads in the industrial, commercial and residential areas in distribution networks requires enhanced reliability and quality of supply. This can be achieved thanks to self healing features of smart grids that already include the control technologies necessary for the restoration strategy in case of a fault. In this paper, an analytical and global optimization model is proposed for the restoration problem. A novel mathematical formulation is presented for the reconfiguration problem reducing the number of required binary variables while covering more practical scenarios compared to the existing models. The considered self healing actions besides the network reconfiguration are the nodal load rejection, the tap setting modification of voltage regulation devices (incl. OLTCs, SVR, and CBs), and the active or reactive power dispatch of DGs. The voltage dependency of loads is also considered. Thus, the proposed optimization problem determines the most efficient restoration plan minimizing the number of deenergized nodes with the minimum number of self healing actions. The problem is formulated as a Mixed Integer Second Order Cone Programming (MISOCP) and solved using the Gurobi solver via the MATLAB interface YALMIP. A real 83 node distribution network is used to test and verify the presented methodology

Using Renewable-Based Microgrid Capabilities for Power System Restoration

Power system restoration (PSR) is a very important procedure to ensure the consumer supply. In this paper, a decentralized multi-agent system (MAS) for dealing with the microgrid restoration procedure is proposed. In this proposed method, each agent is associated to a consumer or microsource (MS) and these will communicate between each other in order to reach a common decision. The agents solve a 0/1 knapsack problem to determine the best load connection sequence during the microgrid restoration procedure. The proposed MAS is tested in two different case studies: a total blackout and a partial blackout, in which the emergency demand response programs are considered. It is developed in the Matlab/Simulink environment and is validated by performing the corresponding dynamic simulations.Power system restoration (PSR) is a very important procedure to ensure the consumer supply. In this paper, a decentralized multi-agent system (MAS) for dealing with the microgrid restoration procedure is proposed. In this proposed method, each agent is associated to a consumer or microsource (MS) and these will communicate between each other in order to reach a common decision. The agents solve a 0/1 knapsack problem to determine the best load connection sequence during the microgrid restoration procedure. The proposed MAS is tested in two different case studies: a total blackout and a partial blackout, in which the emergency demand response programs are considered. It is developed in the Matlab/Simulink environment and is validated by performing the corresponding dynamic simulations

Modeling of Utility Distribution Feeder in OpenDSS with Steady State Impact Analysis of Distributed Generation

With the deregulation of the electric power industry and the advancement of new technologies, the attention of the utilities has been drawn towards adopting Distributed Generation (DG) into their existing infrastructure. The deployment of DG brings ample technological and environmental benefits to the traditional distribution networks. The appropriate sizing and placement of DGs which generate power locally to fulfill consumer demands, helps to reduce power losses and avoid transmission and distribution system expansion.;The primary objective of this thesis is to model a utility distribution feeder in OpenDSS. Studies are conducted on the data obtained from American Electric Power utility. This thesis develops models for 12.47 kV (medium voltage) distribution feeders in OpenDSS by utilizing the existing models in CYMDIST. The model conversion is achieved by a detailed one-to-one component matching approach for multi phased lines, conductors, underground cables, loads, regulators and capacitor banks. The power flow results of OpenDSS and CYMDIST are compared to derive important conclusions.;The second major objective is to analyze the impacts of DG on distribution systems and two focus areas are chosen, namely: effect on voltage profiles and losses of the system and the effects on power market operation. To analyze the impacts of DG on the distribution systems, Photovoltaic (PV) system with varying penetration levels are integrated at different locations along the developed feeder model. PV systems are one of the fastest growing DG technologies, with a lot of utilities in North America expressing interest in its implementation. Many utilities either receive incentives or are mandated by green-generation portfolio regulations to install solar PV systems on their feeders. The large number of PV interconnection requests to the utilities has led to typical studies in the areas of power quality, protection and operation of distribution feeders. The high penetration of PV into the system throws up some interesting implications for the utilities. Bidirectional power flow into a distribution system, (which is designed for one way power flow) may impact system voltage profiles and losses. In this thesis, the effects of voltage unbalance and the losses of the feeder are analyzed for different PV location and penetration scenarios.;Further, this thesis tries to assess the impact of DG on power market operations. In a deregulated competitive market, Generation companies (Genco) sell electricity to the Power exchange (PX) from which large customers such as distribution companies (Disco) and aggregators may purchase electricity to meet their needs through a double sided bidding system. The reliable and efficient operation of this new market structure is ensured by an independent body known as the Independent System Operator (ISO). Under such a market structure, a particular type of unit commitment, called the Price Based Unit Commitment (PBUC) is used by the Genco to determine optimal bids in order to maximize its profit. However, the inclusion of intermittent DG resources such as wind farms by the Gencos causes uncertainty in PBUC schedules. In this research, the effects of intermittency in the DG resource availability on the PBUC schedule of a Genco owning a distribution side wind farm are analyzed

Grid-forming wind power plants

With growing concerns over climate change, the power system is witnessing an unprecedented growth in electricity generation from intermittent renewable energy sources (RES) such as wind and solar, which are commonly interfaced to the grid by power-electronic converters. However, increasing the penetration level of converter-interfaced generation units reduces the number of synchronous generators (SGs) in the grid that provide system services to support voltage and frequency, either inherently or through mandatory requirements and market products. This brings several challenges for the grid operators, which include increasing risk of harmonic interactions, decreasing system inertia and reduction in the short-circuit power of the grid, which all together might jeopardize the security and availability of the power systems. As a countermeasure, it is necessary that the power-electronic-based generation units not only provide grid support services that are originally provided by the SGs, but also operate in harmony with other generation units in all kinds of grid conditions. As a result, the concept of grid-forming (GFM) control, which mimics the beneficial properties of the SGs in converter systems, has emerged as a viable solution to allow effective and secured operation of power systems with increased penetration of converter-based resources.\ua0\ua0 This thesis investigates the application of GFM control strategies in wind power plants (WPPs). In particular, the focus of the work will be on developing an effective GFM control strategy for the energy storage systems (ESS) in WPPs that not only supports the operation of the WPP in various grid conditions, but also offers a certain degree of GFM properties to the overall WPP. To start with, the selection of the most suitable GFM control strategy for wind power applications is made by evaluating and comparing various control strategies available in the literature. The comparison is based on their influence on the frequency characteristics of the converter and robustness of the controller in varying grid strength. To address the transient stability problem of GFM converters during current limitation, a novel strategy based on the limitation of converter\u27s internal voltage vector is developed, which effectively limits the converter current to a desired value and retains the GFM properties of the converter at all times. An experimental setup is used to validate the effectiveness of the proposed limitation strategy in case of various grid disturbances. By implementing the proposed GFM control strategy for the ESS in a test WPP model, it is shown using detailed time-domain simulation results that the GFM behaviour can be offered to the overall WPP. The Network Frequency Perturbation (NFP) plots are used to verify the GFM behaviour of the considered WPP. Furthermore, an overview of various energy storage technologies (ESTs) suitable for providing ancillary services from WPPs is presented. With a focus on the two most suitable ESTs, i.e., batteries and supercapacitors, recommendations are given for design and sizing of the ESS for a given application. Finally, a coordinated control strategy between the WPP and SGs is developed, which facilitates the provision of frequency support from the WPP and at the same time reduces the energy storage requirements for the converter system

Using Wireless Communications To Enable Decentralized Analysis and Control of Smart Distribution Systems

The smart grid is a multidisciplinary approach that aims to revolutionize the whole electricity supply chain including generation, transmission and distribution systems in order to overcome the multiple challenges currently facing the electric power grid. The smart grid could be seen as a modern electrical power grid in which information as well as electricity flows among all nodes in the system, information is continuously collected, processed and hence used to control and coordinate the different system components such as distributed generation (DG) units, capacitor banks, voltage regulating transformers, etc. Therefore distributed intelligence and two-way data communication links are essential components in implementing the smart grid vision. There are numerous research efforts that focus on implementing the smart grid vision in electrical power distribution systems, most of which only target one aspect of the distribution system control and operation, e.g. a control system for voltage control, another one for DG control, a third one for protection, etc. The coexistence of such control strategies in a distribution system raises some concerns about their overall performance, their interactions with the other control strategies, and whether these control systems can adapt to changes in distribution system connectivity. In this PhD thesis we try to address these issues by proposing an implementation of the smart grid vision for distribution systems that provides an integrated design of power systems, communication systems and control strategies. A unified and flexible framework that incorporates all the different aspects of distribution system control and operation is proposed. Distributed processing units equipped with wireless communication capabilities are used to continuously process the local data along with the data received from other nodes and forward the results to neighboring nodes in the system, which in turn process the received data and share the results with their neighbors. Consequently, changes in any of the system components (load values, status of DG etc.) are taken into account in the calculations as soon as they occur, and the results are forwarded to relevant nodes in the systems. This way the information “propagates” throughout the system resulting in a seamless control and coordination among all the system components. Simulation of the electrical power distribution and the communication systems reveal the effectiveness of the proposed framework to control and coordinate multiple capacitor banks, DG units and voltage regulating transformers with changing load levels. It also reveals the potential of the proposed framework to operate in real-time by combining the real-time measured quantities with computer analysis in order to control the different system components within the time frame of normal non-emergency operating conditions. An experimental setup is built and used as a test bed for the proposed framework in order to assess the performance of the different ideas and techniques proposed in this thesis

Monitoring and control requirement definition study for Dispersed Storage and Generation (DSG), volume 1

Twenty-four functional requirements were prepared under six categories and serve to indicate how to integrate dispersed storage generation (DSG) systems with the distribution and other portions of the electric utility system. Results indicate that there are no fundamental technical obstacles to prevent the connection of dispersed storage and generation to the distribution system. However, a communication system of some sophistication is required to integrate the distribution system and the dispersed generation sources for effective control. The large-size span of generators from 10 KW to 30 MW means that a variety of remote monitoring and control may be required. Increased effort is required to develop demonstration equipment to perform the DSG monitoring and control functions and to acquire experience with this equipment in the utility distribution environment

The Application of Superconducting Technologies in Future Electrical Power Systems

Growing power demand in countries such as the UK can often result in increased power losses and voltage control problems within distribution networks. Mitigation of these issues in distribution networks is challenging when conventional power conductors and transformers are considered. There are several methods that may reduce losses in distribution networks, such as carefully sited and operated distributed generation (DG) and distributed control techniques. Since High Temperature Superconductor (HTS) cables exhibit zero resistance when cooled to the boiling point of liquid nitrogen (77Keliven), they have the potential to be used to address these issues in distribution networks. This thesis has investigated the impact of HTS cables and HTS transformers on power losses, voltage changes, fault levels and DG on an existing section of the UK distribution network and compares this with one utilising conventional cables and lines. This study has been accomplished using IPSA. Also, another piece of work calculates in terms of the power losses in HTS cables and HTS transformers including the power needs of their refrigeration systems. This has then been compared these to power losses incurred in conventional distribution and transmission networks. Furthermore, the thesis introduces the comparison costs of HTS cables and HTS transformers with conventional cables and transformers and considers future projected costs for HTS cables and transformers. This information has been used to enable a techno economic evaluation of the potential of future alternative superconductor network design. A method for reactive power sharing in an AC superconductor distribution network, including various DGs, has also been proposal. In addition, this thesis has demonstrated the possibility of increasing the ability of electrical distribution networks to deliver high power densities to critical urban areas, whilst avoiding the need for heavy network reinforcement and additional assets. These studies en achieves using IPSA and Matlab software. Finally, research of work was carried out to investigate the practical effects of installing superconductor equipment and identify novel network designs that make the best use of the attributes of superconducting network assets in terms of lower power losses, lower capital cost and a lower risk level than existing conventional distribution network designs. In 2013, the total cost of the future 33kV superconductor distribution network design would be £842.1M higher than that of the present conventional distribution network design. However, by 2030 the future 33kV superconductor network design will be £16.86 M lower than the present conventional network design. Consequently, these results show that using HTS assets in large distribution network design, operating at different voltage levels could save millions of pounds in the future

Hybrid Energy Storage Implementation in DC and AC Power System for Efficiency, Power Quality and Reliability Improvements

Battery storage devices have been widely utilized for different applications. However, for high power applications, battery storage systems come with several challenges, such as the thermal issue, low power density, low life span and high cost. Compared with batteries, supercapacitors have a lower energy density but their power density is very high, and they offer higher cyclic life and efficiency even during fast charge and discharge processes. In this dissertation, new techniques for the control and energy management of the hybrid battery-supercapacitor storage system are developed to improve the performance of the system in terms of efficiency, power quality and reliability. To evaluate the findings of this dissertation, a laboratory-scale DC microgrid system is designed and implemented. The developed microgrid utilizes a hybrid lead-acid battery and supercapacitor energy storage system and is loaded under various grid conditions. The developed microgrid has also real-time monitoring, control and energy management capabilities. A new control scheme and real-time energy management algorithm for an actively controlled hybrid DC microgrid is developed to reduce the adverse impacts of pulsed power loads. The developed control scheme is an adaptive current-voltage controller that is based on the moving average measurement technique and an adaptive proportional compensator. Unlike conventional energy control methods, the developed controller has the advantages of controlling both current and voltage of the system. This development is experimentally tested and verified. The results show significant improvements achieved in terms of enhancing the system efficiency, reducing the AC grid voltage drop and mitigating frequency fluctuation. Moreover, a novel event-based protection scheme for a multi-terminal DC power system has been developed and evaluated. In this technique, fault identification and classifications are performed based on the current derivative method and employing an artificial inductive line impedance. The developed scheme does not require high speed communication and synchronization and it transfers much less data when compared with the traditional method such as the differential protection approach. Moreover, this scheme utilizes less measurement equipment since only the DC bus data is required