published_or_final_version / Electrical and Electronic Engineering / Master / Master of Philosophy

Increasing penetration of non-dispatchable renewable energy resources and greater peak power demand present growing challenges to Bulk Power System (BPS) reliability and resilience. This research investigates the use of an Internet of Things (IoT) framework for large scale Distributed Energy Resource (DER) aggregation and control to reduce energy imbalance caused by stochastic renewable generation. The aggregator developed for this research is Distributed Energy Resource Aggregation System (DERAS). DERAS comprises two AllJoyn applications written in C++. The first application is the Energy Management System (EMS), which aggregates, emulates, and controls connected DERs. The second application is the Distributed Management System (DMS), which is the interface between AllJoyn and the physical DER. The EMS runs on a cloud-based server with an allocated 8 GB of memory and an 8 thread, 2 GHz processor. Raspberry Pis host the simulated Battery Energy Storage System (BESS) or electric water heater (EWH) DMSs. Five Raspberry Pis were used to simulate 250 DMSs. The EMS used PJM's regulation control signals, RegA and RegD, to determine DERAS performance metrics. PJM is a regional transmission organization (RTO). Their regulation control signals direct power resources to negate load and generation imbalances within the BPS. DERAS's performance was measured by the EMS server resource usage, network data transfer, and signal delay. The regulation capability of aggregated DER was measured using PJM's resource performance assessment criteria. We found the use of an IoT framework for DER aggregation and control to be inadequate in the current network implementation. However, the emulated modes and aggregation response to the regulated control signal demonstrates an excellent opportunity for DER to benefit the BPS.

Advanced power electronic techniques are crucial to enable high-performance energy conversion systems for the applications of various load and source interfaces, e.g., electric vehicle battery charger, solar power, wind power, motor traction, grid-connection. Also, the improvements on electrification for energy conversion contributes to the Carbon Neutrality with the reduction of fuel combustion. The control and design of the power conversion systems largely determine the efficiency, power density and system cost which typically need specialized design procedures. Since the types of interfaced energy sources may vary, the corresponding control algorithms and hardware configurations will be different. Thus, the power electronics system design is conventionally a specific routine based on the desired source and load requirements. Generally speaking, two main perspectives need to be considered when designing a power conversion system: (1) the power converter circuitry topology with the corresponding hardware components, e.g., low/high power circuits design, passive components design; (2) control algorithms and functions design, e.g., voltage/current control techniques, active/reactive power balancing and adjustment. However, the repetitive and specific power electronics design procedures for different load/source requirements are time-consuming and costly. This thesis proposes a software-defined power electronics concept to develop a generalized auto-converter module (ACM) by leveraging variable-frequency critical-soft-switching, model predictive control techniques and high-performance litz-PCB inductors. The software-defined power electronics techniques can be applied to various types of electrified load/source applications without the need of repetitive hardware components and software algorithms designing procedures. The fundamental unit for the generalized concept, auto-converter module, is a type of MPC-based power module. A hierarchical control architecture is designed to manage the local ACMs and satisfy different load/source energy conversion requirements with high efficiency, high power-density and high-reconfigurability. To achieve high-performance for the software-defined power electronics system, several advanced technologies are developed and integrated including variable-frequency critical-soft-switching, modular model predictive control, litz-PCB inductor design. Firstly, a variable-frequency critical-soft-switching technique is developed to adjust the switching frequency for the zero-voltage soft-switching. Doing so, the switching losses can be largely reduced with high efficiency. Secondly, the critical-soft-switching inductor is designed based on litz-PCB winding structure and neural network model to optimize the inductor losses and reduce the volume for the application of high frequency and large current ripple. Thirdly, a modular model predictive control method is designed for each of the local ACM to improve the dynamic performance and attenuate the oscillation caused by the variable frequency operation. Lastly, a hierarchical control architecture is developed to generalize the software-defined power electronics with multi-layer structure, central control layer, local module control layer and application layer. The hierarchical control architecture can be widely applied to different types of load/source interfaces, e.g., single/three-phase grid-connected inverters, motor traction inverter, battery charger, solar energy and so on. Leveraging the hierarchical control architecture and software-defined power electronics, the repetitive power converter hardware components and software algorithms design procedures can be simplified and standardized. Also, for different power converter applications, the efficiency and power density are both improved with better dynamic performance.

Indiana University-Purdue University Indianapolis (IUPUI) / This thesis proposes two new topologies for Uninterrupted Power Supply (UPS), and a grid-tie microinverter. The first topic will discuss an on-line transformerless UPS system based on the integrated power electronics converters that is able to control the input power factor, charge the battery, and guarantee backup operation of the system. The main advantages of the proposed UPS are active power factor correction (PFC) without the need of a complex control scheme, and integrated functions of the battery charger circuit and PFC with only three power switches. Operation modes of the system and the PWM strategy is presented in detail. The second topic discussed is of a proposed circuitry for a single-phase back-to-back converter for UPS applications. The main advantages of this topology is higher number of levels at the rectifier side, less number of power switches, and no need for a boost inductor at the input side of the converter. The last topic discussed is of a proposed patent pending microinverter. This topic was a project funded by the National Science Foundation, and its aim was to help commercialize the research. This project proposes a solution for a solar inverter called Delta Microinverter that allows easier and faster installation as well as power conversion with higher efficiency. Delta Microinverters innovation is found in its patent-pending shape and in its patent-pending circuitry, i.e., electronics mounted inside of the Delta Microinverter. The Delta Microinverters shape has a housing configured for rapid mounting using a single fastener and its power electronics configuration offers an optimized relationship between the number of levels and number of power switches.

A dissertation submitted to the Faculty of Engineering and the Built Environment, University of the Witwatersrand, Johannesburg, in ful lment of the requirements for the degree of Master of Science in Engineering. Johannesburg, 2015 / The work presented extends and contributes to research in Non-Intrusive Load Monitoring (NILM), focussing on steady-state and transient power measurement disaggregation techniques for circuits containing household ap- pliances. Although previous work in this area has produced and evaluated a wide range of NILM approaches, much of it has involved the use of datasets captured from real-world household implementations. In such cases, the lack of accurate ground truth data makes it di cult to assess disaggregation tech- niques. In the research presented, three NILM techniques are comparatively evaluated using measurements from typical household appliances assembled within a laboratory environment, where accurate ground truth data could be compiled to complement the measurements. This allows for the accu- racy of the various disaggregation approaches to be precisely evaluated. It is demonstrated that the correlation of transient event edges in aggregated power measurements to individual appliance transient exemplars performs better than the matching of steady-state power levels against individual ap- pliance state combinations. Furthermore, the transient approach is shown to be the most appropriate technique for further development. / MT2017

Indiana University-Purdue University Indianapolis (IUPUI) / The existing topologies of solar micro inverter use a number of stages before the DC input voltage can be converted to AC output voltage. These stages may contain one or more power converters. It may also contain a diode rectifier, transformer and filter. The number of active and passive components is very high. In this thesis, the design of a new solar micro inverter is proposed. This new micro inverter consists of a new single switch inverter which is obtained by modifying the already existing single ended primary inductor (SEPIC) DC-DC converter. This new inverter is capable of generating pure sinusoidal waveform from DC input voltage. The design and operation of the new inverter are studied in detail. This new inverter works with a controller to produce any kind of output waveform. The inverter is found to have four different modes of operation. The new inverter is modeled using state space averaging. The system is a fourth order system which is non-linear due to the inherent switching involved in the circuit. The system is linearized around an operating point to study the system as a linear system. The control to output transfer function of the inverter is found to be non-minimum phase. The transfer functions are studied using root locus. From the control perspective, the presence of right half zero makes the design of the controller structure complicated. The PV cell is modeled using the cell equations in MATLAB. A maximum power point tracking (MPPT) technique is implemented to make sure the output power of the PV cell is always maximum which allows full utilization of the power from the PV cell. The perturb and observe (P&O) algorithm is the simplest and is used here. The use of this new inverter eliminates the various stages involved in the conventional solar micro inverter. Simulation and experimental results carried out on the setup validate the proposed structure of inverter.