A nanogrid is a standalone hybrid renewable system that uses distributed renewable and non-renewable sources to supply power to local loads. The system is based on power electronics, with interface converters allowing the sources to supply power to the system and the loads to draw power from the system. The nanogrid is typically designed such that renewable sources supply the average load demand, while storage and non-renewable generation are used to ensure that the loads enjoy a continuous supply of power in the presence of the stochastic renewable sources. To maintain the power balance in the system while maximising use of the renewable sources, all sources in the system are scheduled according to a supply-side control law. The renewable sources are used wherever possible and the storage is operated as a slack power bus. The storage is controlled to absorb any excess power from the renewable sources and release it to the system when necessary. The non-renewable generation is only brought online when the storage and renewable sources are incapable of balancing the load demand. While the primary method for maintaining the power balance in the nanogrid is scheduling the sources according to a supply-side control law, a demand-side control law may also be used to help maintain the power balance in the system or protect the system from a complete collapse under overload conditions. A demand-side control strategy is implemented by shedding loads when the load exceeds the available generation, beginning with those loads having the lowest utilisation priority. Hybrid renewable systems are typically designed and controlled in a similar manner to the traditional ac power system, operating at 50/60~Hz, and maintaining the power balance in the system using frequency droop for power sharing and central coordination for scheduling the sources. However a nanogrid has different components compared to the ac system, employing power electronic converters to interface the sources and loads to the system. The control flexibility afforded by the use of power electronic interface converters opens the door to new transmission and control possibilities. This thesis evaluates a number of transmission options ranging from dc to high frequency ac in order to determine an operating frequency that is suitable for this niche system. A number of control topologies are also investigated to find a low cost strategy for implementing a supply-side control law. DC is selected as the operating frequency of choice largely for its simpler source interface requirements. A novel control strategy, dc bus signalling (DBS), is proposed as a means of implementing a supply-side control law. Its distributed structure maintains the modularity inherent in the distributed structure of the nanogrid. DBS uses the voltage level of the dc bus to convey system information. With a supply-side control law implemented using DBS, the source and storage interface converters operate autonomously based on the voltage level of the dc bus. The converters not only respond to the level of the dc bus, but they also change the level of the dc bus, automatically controlling other converters in the system. This thesis presents the theory of operation behind this control strategy and outlines a method for implementing a supply-side control law. A method for ensuring that the supply-side control law operates in a practical system where transmission line impedance affects the information conveyed by the dc bus is also given. For completeness, a method for implementing a demand-side control law using DBS is also presented. A simulation model of a nanogrid is presented and results are obtained to demonstrate the operation of DBS. The design of a small experimental system is also presented, and results are obtained to verify the operation of this new control strategy in a practical system. The simulation and experimental results demonstrate the feasibility of implementing supply and demand-side control laws in a nanogrid using DBS, even in the presence of transmission line impedance.

<p></p><p>The modern U.S. power grid is susceptible to a variety of vulnerabilities, ranging from aging infrastructure, increasing demand, and unprecedented interactions (e.g., distributed energy resources (DERs) generating energy back to the grid, etc.). In addition, the rapid growth of new technologies such as the Internet of Things (IoT) affords promising new capabilities, but also accompanies a simultaneous risk of cybersecurity deficiencies. Coupled with an electrical network referred to as one of the most complex systems of all time, and an overall D+ rating from the American Society of Civil Engineers (ASCE), these caveats necessitate revaluation of the electrical grid for future sustainability. Several solutions have been proposed, which can operate in varying levels of coordination. A microgrid topology provides a means of enhancing the power grid, but does not fundamentally solve a critical issue surrounding energy consumption at the endpoint of use. This results from the necessary conversion of Alternating Current (AC) power to Direct Current (DC) power in the vast majority of devices and appliances, which leads to a loss in usable energy. This situation is further exacerbated when considering energy production from renewable resources, which naturally output DC power. To transport this energy to the point of application, an initial conversion from DC to AC is necessary (resulting in loss), followed by another conversion back to DC from AC (resulting in loss).</p> <p> </p> <p>Tackling these losses requires a much finer level of resolution, namely that at the component level. If the network one level below the microgrid, i.e. the nanogrid, operated completely on DC power, these losses could be significantly reduced or nearly eliminated altogether. This network can be composed of appliances and equipment within a single building, coupled with an energy storage device and localized DERs to produce power when feasible. In addition, a grid-tie to the outside AC network can be utilized when necessary to power devices, or satisfy storage needs. </p> <p> </p> <p>This research demonstrates the novel implementation of a DC nanogrid within a residential setting known as <i>The DC Nanogrid House</i>, encompassing a complete household conversion from AC to DC power. The DC House functions as a veritable living laboratory, housing three graduate students living and working normally in the home. Within the house, a nanogrid design is developed in partnership with renewable energy generation, and controlled through an Energy Management System (EMS). The EMS developed in this project manages energy distribution throughout the house and the bi-directional inverter tied to the outside power grid. Alongside the nanogrid, household appliances possessing a significant yearly energy consumption are retrofitted to accept DC inputs. These modified appliances are tested in a laboratory setting under baseline conditions, and compared against AC equivalent original equipment manufacturer (OEM) models for power and performance analysis. Finally, the retrofitted devices are then installed in the DC Nanogrid House and operated under normal living conditions for continued evaluation.</p> <p> </p> <p>To complement the DC nanogrid, a comprehensive sensing network of IoT devices are deployed to provide room-by-room fidelity of building metrics, including proximity, air quality, temperature and humidity, illuminance, and many others. The IoT system employs Power over Ethernet (PoE) technology operating directly on DC voltages, enabling simultaneous communication and energy supply within the nanogrid. Using the aggregation of data collected from this network, machine learning models are constructed to identify additional energy saving opportunities, enhance overall building comfort, and support the safety of all occupants.</p><br><p></p>

The thesis addresses electronic power distribution systems for the residential applications. Presented are both, renewable energy ac-nanogrid system along with the vehicle-to-grid technology implementation, and envisioned structure and operation of dc-nanogrid addressing all system components chosen as an inherent part of the future electrical architecture. The large-scale model is built and tested in the laboratory environment covering a few operational modes of the ac-nanogrid, while later in the thesis is shown how dc bus signaling technique could be contemplated for the energy management of the renewable energy sources and their maximal utilization. Thesis however puts more focus on the dc-nanogrid system to explore its benefits and advantages for the electrical systems of the future homes that can easily impact not only residential, but also microgrid, grid and intergrid levels. Thus, presented is low frequency terminal behavioral modeling of the system components in dc-nanogrid motivated by the fact that system engineers working on the system-level design rarely have access to all the information required to model converters and system components, other than specification and data given in the datasheets. Using terminal behavioral modeling, converters are measured on-line and their low frequency dynamics is identified by the means of the four transfer functions characteristically used in two port network models. This approach could significantly improve system-level design and simulations. In addition to previously mentioned, thesis addresses terminal behavioral modeling of dc-dc converters with non-linear static behavior showing hybrid behavioral models based on the Hammerstein approach. / Master of Science