A paradigm shift in distribution system design and planning is being led by the deregulation of the power industry and the increasing adoption of distributed generation (DG). Technology advances have made DG investments feasible by both local distribution companies (LDCs) and small power producers (SPPs). LDCs are interested in finding optimal long term plans that best serve their customers at the lowest cost. SPPs, as private entities, are concerned about maximizing their rates of return. Also keenly interested in distribution design and planning is the government, which, through an electricity regulator, strives to meet DG penetration and emissions reduction goals through policy implementations. This thesis first examines the distribution system planning problem from the LDC's perspective. An innovative hierarchical dynamic optimization model is proposed for the planning of distribution systems and the energy scheduling of units that is also capable of reconciling uncoordinated SPP investments in DG. The first stage of the two-stage framework consists of a siting-cum-period planning model that sets element sizing and commissioning dates. The second stage consists of a capacity-cum-production planning model that finalizes element capacities and energy import/export and production schedules. The proposed framework is demonstrated on a 32-bus radial distribution system. Four case studies encompassing different policy sets are also conducted, demonstrating that this model's usefulness also extends to predicting the impact of different energy policies on distribution system operation and economics. The analysis of different policy sets is further expanded upon through the proposal of a new mathematical model that approaches the distribution design problem from the regulator's perspective. Various case studies examining policies that may be used by the regulator to meet DG penetration and emissions goals, through DG investment, are constructed. A combination of feed-in-tariffs, CO$_2$ tax, and cap-and-trade mechanisms are among the policies studied. The results, in the context of Ontario, Canada and its Standard Offer Program, are discussed, with respect to achieving objectives in DG investment, participation by SPPs, consumer costs, and uncertainty in carbon market prices. In jurisdictions such as Ontario, the LDC cannot invest in its own DG capacity but must accommodate those of SPPs. With the successful implementation of DG investment incentives by the regulator, there is a potential for significant investments in DG by SPPs, which may exceed that of the LDCs ability to absorb. This thesis proposes a novel method that can be used by the regulator or LDC to fairly assess, coordinate, and approve multiple competing investments proposals while maintaining operational feasibility of the distribution system. This method uses a feedback between the LDC and SPPs to achieve maximum investor participation while adhering to the technical operational limits of the distribution system. The proposed scheme is successfully demonstrated on a 32-bus radial distribution system, where it is shown to increase SPP-DG investments and production, improve the system's voltage profile, and reduce losses.

The increasing penetration of distributed generation (DG) in power distribution systems presents technical and economic benefits as well as integration challenges to utility engineers. Governments are beginning to acknowledge DG as an economically viable alternative to deferring investment at generation, transmission and distribution levels, meeting demand growth and improving distribution network performance and security. DG technology is rapidly maturing in Ontario due to government economic incentives promoting connection, specifically, the Ontario’s Feed-In-Tariff (FIT) Program. Optimal sizing and siting of DG is well researched, traditionally studying the technical impact on distribution system such as real power loss reduction and voltage profile improvement. Equally common objectives studied are the economics of DG installation which are useful for the developer when deciding when and where to install. Although DG represents a “non-wires” solution to network asset reinforcement, the direct economic benefit to the host utility from promoting DG uptake is not fully understood by utility planners and asset managers. Some DG based asset reinforcement deferral work has been performed in the UK and Italy but is mainly at the transmission level and is not part of an overall strategy that could be applied by a utility. This research presents a comprehensive three stage technique: optimal siting, optimal sizing and financial evaluation of cost savings over a defined planning period to quantify the economic benefit to a Local Distribution Company (LDC) of solar photovoltaic (PV) DG connections on an actual distribution feeder. Optimal sites for PV DG are determined by applying the power loss sensitivity factor method to the test feeder. The objective functions used to determine cost savings consist of loss minimization, asset investment deferral, and peak demand reduction to identify an optimal DG penetration limit. Furthermore, a utility planner can identify an optimal DG penetration limit, encourage uptake at preferred locations that would benefit the LDC, and use the positive impact of DG at existing locations as part of an asset management strategy to prioritize and schedule future asset reinforcement upgrades.

Interest in Distributed Generation (DG) in power system networks has been growing rapidly. This increase can be explained by factors such as environmental concerns, the restructuring of electricity businesses, and the development of technologies for small-scale power generation. DG units are typically connected so as to work in parallel with the utility grid; however, with the increased penetration level of these units and the advancements in unit’s control techniques, there is a great possibility for these units to be operated in an autonomous mode known as a microgrid. Integrating DG units into distribution systems can have an impact on different practices such as voltage profile, power flow, power quality, stability, reliability, and protection. The impact of the DG units on stability problem can be further classified into three issues: voltage stability, angle stability, and frequency stability. As both angle and frequency stability are not often seen in distribution systems, voltage stability is considered to be the most significant in such systems. In fact, the distribution system in its typical design doesn’t suffer from any stability problems, given that all its active and reactive supplies are guaranteed through the substation. However, the following facts alter this situation: • With the development of economy, load demands in distribution networks are sharply increasing. Hence, the distribution networks are operating more close to the voltage instability boundaries. • The integration of distributed generation in distribution system introduces possibility of encountering some active/reactive power mismatches resulting in some stability concerns at the distribution level. Motivated by these facts, the target of this thesis is to investigate, analyze and enhance the voltage stability of distribution systems with high penetration of distributed generation. This study is important for the utilities because it can be applied with Connection Impact Assessment (CIA ). The study can be added as a complement assessment to study the impacts of the installation of DG units on voltage stability. In order to accomplish this target, this study is divided into three perspectives: 1) utilize the DG units to improve the voltage stability margin and propose a method to allocate DG units for this purpose, 2) investigate the impact of the DG units on proximity to voltage stability 3) conduct harmonic resonance analysis to visualize the impacts of both parallel and series resonance on the system’s stability. These perspectives will be tackled in Chapter 3, Chapter 4, and Chapter 5, respectively. Chapter 3 tackles placing and sizing of the DG units to improve the voltage stability margin and consider the probabilistic nature of both the renewable energy resources and the load. In fact, placement and sizing of DG units with an objective of improving the voltage stability margin while considering renewable DG generation and load probability might be a complicated problem, due to the complexity of running continuous load flow and at the same time considering the probabilistic nature of the load and the DG unit’s resources. Therefore, this thesis proposes a modified voltage index method to place and size the DG units to improve the voltage stability margin, with conditions of both not exceeding the buses’ voltage, and staying within the feeder current limits. The probability of the load and DG units are modeled and included in the formulation of the sizing and placing of the DG units. Chapter 4 presents a model and analysis to study the impact of the DG units on proximity to voltage instability. Most of the modern DG units are equipped with power electronic converters at their terminals. The power electronic converter plays a vital role to match the characteristics of the DG units with the requirements of the grid connections, such as frequency, voltage, control of active and reactive power, and harmonic minimization. Due to the power electronics interfacing, these DG units have negligible inertia. Thus, they make the system potentially prone to oscillations resulting from the network disturbances. The main goal of this chapter is to model and analyze the impact of distributed generation DG units on the proximity of voltage instability, with high penetration level of DG units. Chapter 5 studies the harmonic resonance due to the integration of DG units in distribution systems. Normally, the harmonic resonance phenomenon is classified as a power quality problem, however, this phenomenon can affect the stability of the system due to the parallel and series resonance. Thus, the main goal of this chapter is to study and analyze the impact of the integration of distributed generation on harmonic resonance by modeling different types of DG units and applying impedance frequency scan method.

With increased load demands from the customers, substation congestion problems have become inevitable to the utility companies. Instead of expanding related system installations to alleviate the short-term overloads on the facilities, feasibilities of integrating distributed generator (DG) units to defer the possible congestions are of much concern. This thesis presents an optimal location and reliability analyzing scheme for distribution system integrated with DG units, and provides the systematic guidance to utility companies for related operations. The methodology focuses on the substation capacity constraints and provides the optimal DG locations that can alleviate the congestion problem with highest reliability indices. The proposed analyzing scheme can supply valuable assistance to the utility companies and small independent power producers (IPP) for determining the installations and integrations of DG units to defer possible emerging substation expansions.

Distributed generation (DG) and microgrid will play an essential role in the modern power system. They could improve energy efficiency, reduce losses, minimize environmental impacts and enhance power system reliability and stability. Most of the renewable energy applications would require two or three power conversions before power reaches the loads. If the power from DG could be utilized in DC form, the loss could be minimized and system efficiency is improved. Fuel cell, energy storage battery, photovoltaic and power electronic building block (PEBB) are used in this research to set up a DC microgrid. Simulation and hardware implementation are conducted. Techniques studied in this thesis include different power sources interconnection and DC bus voltage and microgrid power controls. Based on the studied results, DC mircogrid integration and system operation schemes are recommended.

Distributed generation (DG) has received much attention recently due to environmental consciousness and rising of the energy efficiency. However, DG interconnecting to low-voltage distribution system may cause voltage variation, and a lot of single-phase DG or single-phase load may result in voltage unbalance. This thesis presents a distributed-STATCOM (D-STATCOM) to alleviate variation of both positive-sequence and negative-sequence voltages at the fundamental frequency. The D-STATCOM operates as susceptance and conductance at the fundamental positive-and negative-sequence frequency, respectively. The susceptance and conductance commands are dynamically tuned according to voltage fluctuation at the installation location. Therefore, the positive-sequence voltage can be restored to the nominal value as well as the negative-sequence voltage can be suppressed to an allowable level. Computer simulations and experimental results verify the effectiveness of the proposed control strategy.

The integration of cogeneration technologies in residential communities has the potential of reducing energy demand and harmful emissions. This study investigated the impact of selected design parameters on the environmental and economic performances of cogeneration systems integrated into residential communities in cold U.S. climates following a centralized or a decentralized integration approach. Parameters investigated include: 1) density, 2) use mix, 3) street configuration, 4) housing typology, 5) envelope and building systems' efficiencies, 6) renewable energy utilization, 7) cogeneration system type, 8) size, and 9) operation strategy. Based on this, combinations of design characteristics achieving an optimum system performance were identified. The study followed a two-phased mixed research model: first, studies of residential community design and three case studies of sustainable residential communities were analyzed to identify key design parameters; subsequently, simulation tools were utilized to assess the impact of each parameter on cogeneration system performance and to optimize the community design to improve that performance. Assessment procedures included: developing a base-line model representing typical design characteristics of U.S. residential communities; assessing the system performance within this model, for each integration approach, using three performance indicators: reduction in primary energy use, reduction in CO2 emissions; and internal rate of return; assessing the impact of each parameter on the system performance through developing 46 design variations of the base-line model representing changes in these parameters and calculating the three indicators for each variation; using a multi-attribute decision analysis methodology to evaluate the relative impact of each parameter on the system performance; and finally, developing two design optimization scenarios for each integration approach. Results show that, through design optimization, existing cogeneration technologies can be economically feasible and cause reductions of up to 18% in primary energy use and up to 42% in CO2 emissions, with the centralized approach offering a higher potential for performance improvements. A significant correlation also existed between design characteristics identified as favorable for cogeneration system performance and those of sustainable residential communities. These include high densities, high mix of uses, interconnected street networks, and mixing of housing typologies. This indicates the higher potential for integrating cogeneration systems in sustainable residential communities.

This thesis presents the applications of a series interconnection scheme for small distributed generation (DG) systems in distribution networks. The concept uses one set of voltage source converter (VSC) to control the injected voltage magnitude and phase angle for power injection and voltage sag mitigation. Through an energy storage device and the VSC, DG outputs vary concurrently with the line loading and provide load leveling functions. Under voltage sag situations, it provides missing voltages to effectively deal with power quality problems. Due to its series connection characteristic, it is convenient in preventing islanding operation and good for fault current limiting. The concept is suitable for locations where the voltage phase shift is not a major concern. Due to the use of only one set of converter, it is economic for customer site distributed energy resource applications and its control strategy would depend on the types of load connected.

This thesis investigates the impact of high-level penetration of distributed generation especially from the renewable energy sources on the transient stability of the transmission system. Distributed generation is a source of electric power connected to the distribution network or on the consumer side. It is expected that distributed generation grows significantly by the increasing environmental concerns and deregulation in the market. As soon as the increasing penetration level, distributed generation starts to influence the distribution system as well as the transmission system. To investigate the impact of distributed generation with different penetration levels on the transmission system transient stability, simulation scenarios are created and simulations are run on the basis of these scenarios by the implementation of the different distributed generation technologies to the &ldquo / New England&rdquo / test system. Stability indicators are observed to assess the impact on the transient stability. Results are presented throughout the thesis and the impact of the different distributed generation technologies and the different penetration levels on the transient stability is discussed by comparing the stability indicators.

Increased Distributed Generation (DG) presence on radial distribution feeders is becoming a common trend. The existing Overcurrent Protection (OCP) scheme on such feeders consists mainly of overcurrent protection devices (OCPDs) such as fuses and reclosers. When DG is placed on the remote end of a 3-phase lateral, the radial configuration of the feeder is lost. As a result, OCP issues may arise which lead to permanent outages even when the fault is temporary. This thesis presents a new approach that revises the existing OCP scheme of a radial feeder to address the presence of DG. The fuses on the laterals with DGs are removed and multifunction recloser/relays (MFRs) are added to address three specific OCP issues; fuse fatigue, nuisance fuse blowing, and fuse misoperation. The new approach requires no communication medium, provides backup protection for the DG unit, and allows the remaining laterals to retain their existing protective devices. The results are reported using the IEEE 34 node radial test feeder to validate the new approach and the IEEE 123 node radial test feeder to generalize the approach. The new approach completely mitigated the fuse misoperation and nuisance fuse blowing issues and most of the fuse fatigue issues that were present on the radial test feeders. Specifically, the approach demonstrates that coordination between the existing protection devices on radial distribution feeders is maintained in the presence of DG.