Power Electronic Building Block (PEBB) concept is to provide generic building blocks for power conversion, regulation and distribution with control intelligence and autonomy. A comprehensive modeling and analysis of a PEBB based DC distributed power system (DPS), comprising of a front end power factor correction (PFC) boost rectifier, a DC-DC converter and a three phase four leg inverter is performed. All the sub-systems of the DC DPS are modeled and analyzed for stability and good transient performance. A comprehensive stability analysis of a PEBB based DC DPS is performed. The effect of impedance overlap on the system and individual sub-systems is examined. Ability of a PEBB based converter to stabilize the integrated system by actively changing the system bandwidth is presented. The fault tolerance capability in a PEBB based rectifier is established by ensuring stable system operation, with one leg of the rectifier failed open-circuited. / Master of Science

This project examines the implications of the photovoltaic power generation as well as the battery storage systems on the distribution network tariff structures. Different types of existing distribution tariffs were applied to the residential households’ demand patterns. Several scenarios of demand profiles were theoretically investigated. First scenario included households’ consumption under current situation without on-site power production and any storage, second scenario concerned penetration of average size of solar panel installations and the last demand profile with maximum possible size of photovoltaic panels complemented with battery storage use. The distribution tariffs included in the comparison are: power based tariff and two energy based tariffs, one with flat-rate and another with time-of-use structure. Distribution tariffs were normalized with the aim to research the implications of the on-site production and storage use. Normalization factors were used when comparing financial bills from the households under above mentioned scenarios. Energy distribution tariffs have higher potential for households to save on their energy bill with the introduction of the on-site solar power utilization. On the other hand power tariff provides higher incentive for the implementation of the demand response strategies in the households.

Power conversion system design issues are expanding their role in information technology equipment design philosophies. These issues include not only improving power conversion efficiency, but also increased concerns regarding the cost and complexity of the power conversion design techniques utilized to satisfy the host system's total performance requirements. In particular, in computer system (personal computers, workstations, and servers) designs, the power "supplies" are rapidly becoming a limiting factor in meeting overall design objectives. This dissertation addresses the issue of simplifying the architecture of distributed power systems incorporated into computing equipment. In the dissertation's first half, the subject of the design of the distributed power system's front-end converter is investigated from the perspective of simplifying the conversion process while simultaneously improving efficiency. This is initially accomplished by simplifying the second-stage DC/DC converter in the standard two-stage front-end design (PFC followed by DC/DC conversion) through the incorporation of secondary-side control. Unique modifications are then made to two basic topologies (the flyback and boost converter topologies) that enable the two-stage front-end design to be reduced to an isolated PFC conversion stage, resulting in a front-end design that features reduced complexity and higher efficiency. In the dissertation's second half, the overall DC distributed power system design concept is simplified through the elimination of power processing conversion steps - the result being the creation of a high-frequency (HF) AC distributed power system. Design techniques for generating, distributing, and processing HF AC power in this new system are developed and experimentally verified. Also, an experimental comparison between both DC and AC distributed power systems is performed, illustrating in a succinct fashion the merits and limitations of both approaches. / Ph. D.

This dissertation examines the effects of instantaneous constant-power loads (CPLs) on power converters. These CPLs are prevalent in distributed power architectures and are also present in certain motor-drive applications. CPLs introduce a destabilizing nonlinear effect on power converters through an inverse voltage term that leads to significant oscillations in the main bus voltage or to its collapse. Boundary control is studied in order to stabilize dc-dc converters with instantaneous CPLs. The three basic topologies are studied: buck, boost, and buck-boost. Converter dynamics are analyzed in both switching states and the various operating regions of switch interaction with a first-order switching surface are identified. The analysis reveals important characteristics of CPLs. For non-minimum phase converters, in order to avoid issues related with the fact that the closed-loop state-dependent switching function is undefined on the switching surface, reflective mode solutions to both converter systems are defined in the sense of Filippov. Sufficient conditions for large-signal stability of the closed loop converter operating points are established. It is shown that first-order switching surfaces with negative slopes achieve large-signal stability, while positive slopes lead to instability. In particular, for the boost converter it is illustrated via simulations and experiments that positive slopes may lead to another closed-loop limit cycle. It is also shown that instability as well as system-stalling, which is termed the invariant-set problem, may still occur in reflective mode. However, a hysteresis band that contains the designed boundary may be used to prevent system-stalling, and also allow for a practical implementation of the controller by avoiding chattering. Regulation is also achieved. The dynamic behavior of single-phase full-wave uncontrolled rectifiers with instantaneous CPLs is also explored. Stable operation is shown to be dependent on initial condition and circuit parameters, which must fall within reasonable ranges that validate a CPL model. A necessary condition for stable operation of the rectifier system is thus derived. Furthermore, input and output characteristics of the rectifier with a CPL are investigated, and comparisons are made with the resistive case. A more complete model for the rectifier system that incorporates line-voltage distortion is also utilized to study the rectifier system. Simulations and experimental results are included for verification. / text

Paralleling operation of DC/DC converters is widely used in today's distributed power systems. To ensure balanced output currents among paralleled power modules, current sharing control is usually necessary.Active current sharing controls with current feedback mechanism are widely used in today's power supplies. However, the dynamic performance of these current sharing control schemes are not yet clearly explored. In this work, the dynamic current sharing performance is evaluated for paralleling systems with the output impedance approach. As the representative of the terminal characteristic of a power converter, output impedance is a powerful tool to study the dynamic response under load transients. The dynamic current sharing analyses are then conducted for three different active current sharing control structures and a comprehensive comparison among them helps the designer to choose appropriate controls for different applications. On the other hand, high-frequency load transients are possible to happen for voltage regulators, which are the power supplies of microprocessors. In order to study the dynamic current sharing performance for a paralleling system when the perturbation frequency is higher than half of the switching frequency,the conventional output impedance concept needs to be extended. Due to the non-linear behavior of a switching modulator, the beat-frequency phenomenon could cause unexpected failure of a power supply when the perturbation frequency is close to the switching frequency. To address this issue, an unconventional multi-frequency model is proposed for high-frequency dynamic current sharing studies. With this model, the sideband components are possible to be included and the beat-frequency oscillations can be predicted. After that, the conventional impedance concept is expanded in the form of extended describing function, so that the terminal characteristics of paralleled converters are represented by a series of impedances. Besides the analyses, this work also proposed several solutions for the beat-frequency oscillation issue which are experimentally verified. In summary, both low-frequency and high-frequency dynamic current sharing performances are studied in this dissertation. The output impedance concept and its extension in the form of extended describing function are utilized as the tools for researches. With these powerful tools, more insights are obtained to help better design of a paralleling system. / Ph. D.

In the early 1990's, with the boom of the Internet and the advancements in telecommunications, the demand for high-speed communications systems has reached every corner of the world in forms such as, phone exchanges, the internet servers, routers, and all other types of telecommunication systems. These communication systems demand more data computing, storage, and retrieval capabilities at higher speeds, these demands place a great strain on the power system. To lessen this strain, the existing power architecture must be optimized. With the arrival of the age of high speed and power hungry microprocessors, the point of load converter has become a necessity. The power delivery architecture has changed from a centralized distribution box delivering an entire system's power to a distributed architecture, in which a common DC bus voltage is distributed and further converted down at the point of load. Two common distributed bus voltages are 12 V for desktop computers and 48 V for telecommunications server applications. As industry strives to design more functionality into each circuit or motherboard, the area available for the point of load converter is continually decreasing. To meet industries demands of more power in smaller sizes power supply designers must increase the converter's switching frequencies. Unfortunately, as the converter switching frequency increases the efficiency is compromised. In particular, the switching, gate drive and body diode related losses proportionally increase with the switching frequency. This thesis introduces a loss saving self-driven method to drive the secondary side synchronous rectifiers. The loss saving self-driven method introduces two additional transformers that increase the overall footprint of the converter. Also, this thesis proposes a new magnetic integration method to eliminate the need for the two additional gate driver magnetic cores by allowing three discrete power signals to pass through one single magnetic structure. The magnetic integration reduces the overall converter footprint. / Master of Science

As distributed generation penetrates the electric power grid at higher power levels, grid interface issues with distributed generation must be addressed. The current power system consists of central power generators, while the future power system will include many more distributed resources. The centralized power generation system is controlled by utility operators, but many distributed resources will not be controlled by utility operators. Distributed generation must use smart control techniques for high reliability and ideal grid interface. This thesis discusses the grid interface issue of anti-islanding. An electric island occurs when a circuit breaker in the electric power system trips. The distributed resource should disconnect from the electric grid for safety reasons. This thesis will give an overview of the possible methods. Each method will be analyzed using the ability to detect under the non-detection zone and the economic feasibility of the method. This thesis proposes two addition cases for analysis that exist in the electric power system: the effect of multiple methods in parallel in the non-detection zone and the possibility of a false trip caused by a load step. Multiple methods in parallel are possible because the islanding detection method is patentable, so each grid interface inverter company is likely to implement a different islanding detection method. The load step represents a load change when a load is switched on. / Master of Science

Small satellites and CubeSats have established themselves within the aerospace community because of their low cost and high return on investment. Many CubeSats are developed in a short time frame and often leverage commercial off the shelf components for quick turnaround missions. With regard to the Electrical Power System, commercially available products typically use a centralized architecture. However, a centralized architecture is not reusable, since missions that require additional solar arrays or batteries would necessitate a redesign of the power system. With the range of CubeSat sizes and mission goals, it is obvious that a one-size-fits-all solution is not appropriate. This thesis details a reusable and scalable power system architecture applicable to a variety of missions. Reusability is achieved by using common building blocks or "modules," where the same modules can be used between missions. Scalability is achieved by not limiting the number of modules that can be connected together—more modules can be added as needed. In this system, solar arrays and battery units connect directly to a common bus, supplying an unregulated voltage to each subsystem. These subsystems then regulate the bus voltage to their individual needs. The power system also features direct energy transfer and solar-only operation.

In this dissertation, several volt-var optimization methods have been proposed to improve the expected performance of the distribution system using distributed renewable energy sources and conventional volt-var control equipment: photovoltaic inverter reactive power control for chance-constrained distribution system performance optimisation, integrated distribution system optimization using a chance-constrained formulation, integrated control of distribution system equipment and distributed generation inverters, and coordination of PV inverters and voltage regulators considering generation correlation and voltage quality constraints for loss minimization. Distributed generation sources (DGs) have important benefits, including the use of renewable resources, increased customer participation, and decreased losses. However, as the penetration level of DGs increases, the technical challenges of integrating these resources into the power system increase as well. One such challenge is the rapid variation of voltages along distribution feeders in response to DG output fluctuations, and the traditional volt-var control equipment and inverter-based DG can be used to address this challenge. These methods aim to achieve an optimal expected performance with respect to the figure of merit of interest to the distribution system operator while maintaining appropriate system voltage magnitudes and considering the uncertainty of DG power injections. The first method is used to optimize only the reactive power output of DGs to improve system performance (e.g., operating profit) and compensate for variations in active power injection while maintaining appropriate system voltage magnitudes and considering the uncertainty of DG power injections over the interval of interest. The second method proposes an integrated volt-var control based on a control action ahead of time to find the optimal voltage regulation tap settings and inverter reactive control parameters to improve the expected system performance (e.g., operating profit) while keeping the voltages across the system within specified ranges and considering the uncertainty of DG power injections over the interval of interest. In the third method, an integrated control strategy is formulated for the coordinated control of both distribution system equipment and inverter-based DG. This control strategy combines the use of inverter reactive power capability with the operation of voltage regulators to improve the expected value of the desired figure of merit (e.g., system losses) while maintaining appropriate system voltage magnitudes. The fourth method proposes a coordinated control strategy of voltage and reactive power control equipment to improve the expected system performance (e.g., system losses and voltage profiles) while considering the spatial correlation among the DGs and keeping voltage magnitudes within permissible limits, by formulating chance constraints on the voltage magnitude and considering the uncertainty of PV power injections over the interval of interest. The proposed methods require infrequent communication with the distribution system operator and base their decisions on short-term forecasts (i.e., the first and second methods) and long-term forecasts (i.e., the third and fourth methods). The proposed methods achieve the best set of control actions for all voltage and reactive power control equipment to improve the expected value of the figure of merit proposed in this dissertation without violating any of the operating constraints. The proposed methods are validated using the IEEE 123-node radial distribution test feeder.

The research focus of this thesis is on modelling techniques for river kinetic turbines, to develop predictive numerical tools to further the design of this emerging hydro technology. The performance benefits of enclosing the turbine in a shroud are quantified numerically and an optimized shroud design is developed. The optimum performing model is then used to study river kinetic turbines, including different anchoring systems to enhance performance. Two different turbine numerical models are studied to simulate the rotor. Four different computational fluid dynamics (CFD) turbulence models are compared against a series of particle image velocimetry (PIV) experiments involving highly-separated diffuser-flow and nozzle-flow conditions. The risk of cavitation is briefly discussed as well as riverbed boundary layer losses. This study is part of an effort to develop this emerging technology for distributed power generation in provinces like Manitoba that have a river system well adapted for this technology. / May 2007