Doctor of Philosophy / Department of Electrical and Computer Engineering / Anil Pahwa / Power distribution systems are transitioning from traditional centralized-control distribution grids to the modern distribution grids that are more customer-interactive and include microgrids (MGs) as well as various unpredictable and multi-scale distributed energy resources (DERs). However, power fueled by renewable DERs such as wind and solar is highly variable and high penetration of renewable DERs in distribution system may potentially degrade the grid reliability and power quality. Moreover, the growth of such generation sources will increase the number of variables and cause scalability concerns for distribution system operators (DSOs) in handling system optimization problems. Further, with development of MGs, DSO and MG may have different owners and schedule renewable and non-renewable DERs based on their own economic rules and policies while secure and economic operation of the entire system is necessary. The widespread integration of wind and solar and deployment of MGs in distribution system make the task of distribution system operation management quite challenging especially from the viewpoint of variability, scalability, and multi-authority operation management. This research develops unique models and methodologies to overcome such issues and make distribution grid operation, optimization and control more robust against renewable intermittency, intractability, and operation complexity. The objectives of this research are as follows: 1) to develop a three-phase unbalanced large-scale distribution system to serve as a benchmark for studying challenges related to integration of DERs, such as scalability concerns in optimization problems, incremental power losses, voltage rise, voltage fluctuations, volt/var control, and operation management; 2) to develop a novel hierarchical and multilevel distributed optimization for power loss minimization via optimal reactive power provisioning from rooftop PVs which addresses the scalability issues with widespread DER integration in large-scale networks; 3) to develop a dynamic operational scheme for residential PV smart inverters to mitigate the fluctuations from rooftop PV integration under all-weather-condition (fully sunny, overcast and transient cloudy days) while increasing network efficiency in terms of power losses, and number of transformer load tap changer (LTC) operation; 4) to develop a stochastic energy management model for multi-authority distribution system operating under uncertainty from load and wind generation, which is able to precisely account interactions between DSO and MGs.

Phasor measurement is a growth technology in the power grid industry. With new funding, grid reliability concerns, and power capacity margin motivating a smart grid transformation, phasor measurement and smart metering are taking center stage as the implementation methods for grid intelligence. This thesis proposes a novel concept for designing a next generation phasor measurement unit. The present generation phasor measurement unit relies upon venerable existing current and voltage transducer technology that is expensive, bulky, and not well suited to the modern age of digital and computerized control signals. Also, the rising proliferation of installed phasor measurement units will soon result in data overload and huge obligations for network bandwidth and processing centers. This brute-force approach is ill-advised. Forward thinking is required to foresee the future grid, its fundamental operation, and its sensor controller needs. A reasonably safe assumption is a future grid containing sensors numbering in the thousands or millions. This number of sensors cannot transmit raw data over the network without requiring enormous network capacity and data center processing power. This thesis proposes a novel concept—combining existing technologies such as improved current transducers and wireless precision time protocols to design a next generation phasor measurement unit. The unit is entirely self-contained. It requires no external connections due to inclusion of high performance transducers, processor, wireless radio, and even energy harvesting components. With easy, safe, and low cost installation, proliferation of thousands or millions of sensors becomes feasible. Also, with a scalable sensor network containing thousands or millions of parallel distributed processors, data reduction and processing within the network relieves the need for high bandwidth data transmission or supercomputing data centers.

Fault location in distribution systems is a critical component of outage management and service restoration, which directly impacts feeder reliability and quality of the electricity supply. Improving fault location methods supports the Department of Energy (DOE) “Grid 2030” initiatives for grid modernization by improving reliability indices of the network. Improving customer average interruption duration index (CAIDI) and system average interruption duration index (SAIDI) are direct advantages of utilizing a suitable fault location method. As distribution systems are gradually evolving into smart distribution systems, application of more accurate fault location methods based on gathered data from various Intelligent Electronic Devices (IEDs) installed along the feeders is quite feasible. How this may be done and what is the needed methodology to come to such solution is raised and then systematically answered. To reach this goal, the following tasks are carried out: 1) Existing fault location methods in distribution systems are surveyed and their strength and caveats are studied. 2) Characteristics of IEDs in distribution systems are studied and their impacts on fault location method selection and implementation are detailed. 3) A systematic approach for selecting optimal fault location method is proposed and implemented to pinpoint the most promising algorithms for a given set of application requirements. 4) An enhanced fault location method based on voltage sag data gathered from IEDs along the feeder is developed. The method solves the problem of multiple fault location estimations and produces more robust results. 5) An optimal IED placement approach for the enhanced fault location method is developed and practical considerations for its implementation are detailed.

Although modern society is critically reliant on power grids, even modern power grids are subject to unavoidable outages due to storms, lightning strikes, and equipment failures. The situation in developing countries is even worse, with frequent load shedding lasting several hours a day due to unreliable generation. We study the use of battery storage to allow a set of homes in a single residential neighbour- hood to avoid power outages. Due to the high cost of storage, our goal is to choose the smallest battery size such that, with high target probability, there is no loss of power despite a grid out- age. Recognizing that the most common approach today for mitigating outages is to use a diesel generator (genset), we study the related problem of minimizing the carbon footprint of genset operation. Drawing on recent results, we model both problems as buffer sizing problems that can be ad- dressed using stochastic network calculus. We show that this approach greatly improves battery sizing in contrast to prior approaches. Specifically, a numerical study shows that, for a neigh- bourhood of 100 homes, our approach computes a battery size, which is less than 10% more than the minimum possible size necessary to satisfy a one day in ten years loss probability (2.7 ∗ 10^4 ). Moreover, we are able to estimate the carbon footprint reduction, compared to an exact numerical analysis, within a factor of 1.7. We also study the genset scheduling problem when the rate of genset fuel consumption is given by an affine function instead of a linear function of the current power. We give alternate scheduling, an online scheduling strategy that has a competitive ratio of (k1 G/C +k2)/(k1+k2) , where G is the genset capacity, C is the battery charging rate, and k1, k2 are the affine function constants. Numerically, we show that for a real industrial load alternate scheduling is very close to the offline optimal strategy.

The development of future smart electricity grids is driven by efficiency and climate targets and economic benefit for producers, retailers and customers on the deregulated electricity market. Since most investments will be made by grid owners acting as regulated monopolies, it is unclear how they will get return on their investments. Can demand response programs create cost reductions for the grid owner that help motivate the investment in smart grids? Two cases of cost reduction opportunities are evaluated assuming that peak loads are reduced by a demand response program: optimization of cable dimensions for lower peak loads when building new grids, and avoided investments in reinforced capacity in the existing grid. Potential cost reductions are estimated for the two example cases, using financial and technical data for Fortum's local distribution grid in Stockholm. The result shows that reducing the capacity in the cables by 70-80 % only brings down investment costs by 3-4 %, since the common expense for excavation outweighs the incremental cost of cables. Over-capacity means increased redundancy and flexibility to increase load in the future, which are valuable features for a grid owner.Regarding investments in the existing grid, a substation that needs replacement because of overload is analyzed. Assuming a continued trend of steadily increasing load, a 34 % peak load reduction would delay the investment 20 years, which is in turn worth 900,000 SEK in 2010 prices.

This master thesis was provided by ABB Cooperate Research in Västerås. This study has two major purposes: (1) to identify the characteristics of a flywheel energy storage system (FESS), (2) take the first steps in the development of a simulation model of a FESS. For the first part of this master thesis a literature reviews was conducted with focus on energy storage technologies in general and FESS in particular. The model was developed in the simulation environment PSCAD/EMTDC; with the main purpose to provide working model for future studies of the electrical dynamics of a flywheel energy storage system. The main conclusion of the literature review was that FESS is a promising energy storage solution; up to multiple megawatt scale. However, few large scale installations have so far been built and it is not a mature technology. Therefore further research and development is needed in multiple areas, including high strength composite materials, magnetic bearings and electrical machines. The model was implemented with the necessary control system and tested in a simulation case showing the operational characteristics.

With the world suffering from energy crisis, Smart Grid is the expanding research topic that deals vigorously with the current problems. It promotes decentralized renewable energy generation system, participate many local energy producers to energy market, adds vehicle to grid (V2G), minimize the energy loss in the electrical system, and participate many active consumers to the real market. It is an emerging project that needs an expert from many fields, thus it opens door of opportunities for many people around the globe. The present thesis deals with the communication scenario in smart grid. Communication is the backbone of Smart Grid and the thesis tries to highlight the available communication technologies for smart grid application. The thesis discuss most profitable communication technologies used for this purpose which are power line communication and wireless communication, in which power line communication aspects and characteristics are covered more than wireless communication for its use are seen more in upcoming days. In all the thesis will outline the opportunities and challenges of power line communication and wireless communication for smart grid application.

Recently, there have been many initiatives to incorporate advanced controls, two way communications, digital technologies and advanced power system components in the operation and control of power distribution systems. These initiatives are aiming to realize what becomes known as the “Smart grid”. It is expected that a Smart Grid will lead to enhancement in the reliability and efficiency of the power system. The movement towards the Smart Grid is motivated by many factors; the need to integrate more renewable power to mitigate the global warming, the increasing interest in connecting more distributed generation (DG) as a way to postpone large investment in transmission and bulk generation, and the need to increase the reliability of the power system overall to minimize disturbance costs. It is the overall goal of this research to introduce novel distribution system operation techniques to assist in the effort of realizing the “Smart Distribution System” in both normal and system restoration modes. In particular, three main operation functions are dealt with in this research work; Voltage Control, Reactive Power Control and Distribution System Restoration. First for Voltage Control, a reliable and efficient method is proposed to control voltage regulators in order to enable the regulation of multiple feeders with diversified loads using only one regulator provided that no DG is connected to the feeders. Regulator’s tap is selected based on the solution of an integer linear optimization problem. The method has a closed form solution for the optimal tap; that is valuable for real time operation. In addition, necessary condition for feasible solutions is examined. Next, a novel coordinated voltage control scheme is proposed to enable the voltage regulator to efficiently regulate the voltage of multiple feeders in the presence of DGs. The proposed technique is based on placing a Remote Terminal Unit (RTUs) at each DG and each line capacitor. These RTUs coordinate together, through communication, and form a multi-agent system. An important contribution of this research is that the proposed scheme provides the minimum hardware requirement to efficiently estimate the voltage profile of a feeder with DGs. The proposed scheme enables the integration of more DGs into the system by, efficiently, coordinating the operation of voltage regulators and DGs to mitigate voltage rise problem caused by the connection of DGs to the system. Second, for Reactive Power Control, a decentralized reactive power control scheme is proposed to optimally control switched shunt capacitors of the system in order to minimize system losses and maintain acceptable voltage profile. The proposed algorithm provides capacitors with “Advanced Voltage Sensing” capability to enable capacitors to switch in and out according to the global minimum and maximum voltage of the feeder. The proposed technique utilizes the same RTU used for voltage control and relies on the voltage profile estimation technique proposed in this research for the coordinated voltage control. In addition, novel decentralized algorithm is proposed to estimate the feeder voltage profile change as a result of injecting reactive power at the capacitor bus. The proposed reactive power control scheme can be used to coordinate the operation of any number of capacitors connected to the distribution system. Combining voltage control and reactive power control schemes, generalized coordinated voltage control is proposed to coordinate between DGs, shunt capacitors and voltage regulators in order to achieve optimal voltage control for the distribution system and solve the steady state voltage rise problem caused by the connection of DGs, hence, allowing more DGs to be connected to the system. Over and above, the proposed generalized coordinated voltage control enables the realization of a new operation-time DG connection impact assessment concept. Based on this concept, the system will carry out a real-time assessment and decide, based on the available control actions, the maximum DG power that can be allowed to connect to the system at particular operating conditions. This new concept will allow great flexibility to the connection of DGs, most notably, when, due to a change in system configuration, the DG is needed to be connected to a feeder other than the one it was planned for during the planning stage. The last operation function dealt with in this research work is the distribution system restoration. Novel decentralized distribution system restoration scheme is proposed. The proposed scheme is based on dividing the distribution system into zones based on the availability of disconnecting switches. Each zone is controlled by an Agent. The restoration is done based on the coordination between these Agents. Proposed communication protocols between Agents are discussed in details. The goal of the proposed restoration scheme is to maximize the restored power while preserving the radial structure of the distribution system and without exceeding the thermal limit of any equipment in the system. As the proposed technique does not assume any supervision from any central point, this technique will enable the realization of a self-healing distribution system restoration.

Smart grid is an advanced electrical grid equipped with communication capability which is utilized to improve the efficiency, reliability, and sustainability of electricity services. Countries within Europe, North America and East Asia are undergoing a transformation from an antiquated infrastructure to the smart grid. However, some of problems arise due to the security and privacy issues of smart grid. Since smart meters and a grid operator can interact through its communication channel, there is a possibility that a hacker can hack into the system to steal information or even cut off the electricity service. Moreover, people are protesting and refusing to use smart meter since it enables the grid operator to perform frequent meter reading which unveils the customers¡¦ private energy usage information that could be abused. To cope with the privacy issue, we proposed an enhanced version of aggregation protocol from Garcia-Jacobs protocol where our protocol protects not only customers¡¦ energy consumption information but also the consumption information of a neighborhood. Furthermore, we proposed a novel privacy preserving billing protocol based on Priced Oblivious Transfer (POT) protocol which guarantees the grid operator to get the correct amount of money without knowing the individual energy consumption of the customers. Additionally, we also implement our proposed protocols.

In recent years, due to the issues of energy saving, the smart grid has become more important. AMI (Advanced Metering Infrastructure) is the basic of smart grid. However, AMI¡¦s network initialization usually cost a lot of time delay and energy waste because of many collisions due to the initialization in the high node density and variable network. In this paper, we proposed a Dynamic Contention Slot Initialization Protocol (DCSI Protocol) to reduce time delay and energy waste in the network initialization. At the beginning, all nodes in DCSI protocol are set in the receiving state. The proposed approach reduces not only collisions but also the communication failure due to the interference out of the transmission range. We divided time into time slots and then composed them to superframe. The first slot of superframe is designed for master node¡¦s broadcast, and other time slots are devised for other nodes to join in the network. Based on the previous superframe, nodes for the proposed protocol adjust the number of the contention slot by detecting collisions to adapt the high node density and variable network. The simulation results demonstrate superiority of DCSI protocol over flooding.