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

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.

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.

The basic Power Electronics Building Block (PEBB) configurations are identified and conceptual PEBB modules are constructed and tested. Using the INCA (Inductance Calculator) parasitic extraction and the Saber circuit simulation software, the microscopic relationships between the parasitics of the packaging layout and their circuit electrical effects are cross-examined. The PEBB module with advanced packaging techniques is characterized in comparison with the wire-bond module. The soft-switching techniques are evaluated for PEBB applications. The Zero-Current-Transition (ZCT) is proved better because the parasitics in the power current flow path are absorbed into the resonant soft-switching operation. This makes the PEBBs insensitive to system integration. Based on the building block concept, the discrete and large signal average models are developed for simulation, design, and analysis of large-scale PEBB-based systems. New average models are developed for half-bridge PEBB module and Space Vector Modulation (SVM). These models keep the exact information of the discontinuous SVM and the common mode component of the three-phase system. They can be used to construct the computer models of a power electronics system the same as the modularized hardware and perform time domain simulations with very fast speed. Further more, even though the system is modeled based on modularized concept on the ABC coordinates, it can be used to perform small signal analysis on the DQ coordinates as well. Based on the developed models, the system-level interactions in integrated systems are investigated. Three interaction scenarios are presented: (1) the zero-sequence circulation current in paralleled three-phase rectifiers caused by the interleaved discontinuous SVM, (2) the load and source interactions caused by unbalanced load and small signal impedance overlap, and (3) the combined common mode noise caused by both front-end PWM rectifiers and load inverters. The interaction phenomena and mitigation methods are demonstrated through hardware testbed system. The concept of dc bus conditioning is proposed. The bus conditioner is a bi-directional dc/dc converter programmed as a current controlled current source, which shunts the large signal ac current, which otherwise goes to the dc bus, into an isolated energy storage component. In addition to alleviate the source and load interactions, it increases the load impedance/decreases the bus impedance and provides more stability margins to the distribution system. The dc bus conditioner concept and its functions are demonstrated through system simulation and preliminary hardware experiment. / Ph. D.

With the fast advance in VLSI technology, smaller, more powerful digital system is available. It requires power supply with higher power density, lower profile and higher efficiency. PWM topologies have been widely used for this application. Unfortunately, hold up time requirement put huge penalties on the performance of these topologies. Also, high switching loss limited the power density achievable for these topologies. Two techniques to deal with hold up time issue are discussed in this dissertation: range winding solution and asymmetric winding solution, the efficiency at normal operation point could be improved with these methods. To reduce secondary rectifier conduction loss, QSW synchronous rectifier is developed, which also helps to achieve ZVS for symmetrical half bridge converter. Although with these methods, the efficiency of front end DC/DC converter could be improved, the excessive switching loss prohibited higher switching frequency. To achieve the targets, topologies with high switching frequency and high efficiency must be developed. Three resonant topologies: SRC, PRC and SPRC, are been investigated for this application because of their fame of low switching loss. Unfortunately, to design with hold up requirement, none of them could provide significant improvements over PWM converter. Although the negative outcome, the desired characteristic for front end application could be derived. Base on the desired characteristic, a thorough search is performed for three elements resonant tanks. LLC resonant topology is found to posses the desired characteristic. From comparison, LLC resonant converter could reduce the total loss by 40% at same switching frequency. With doubled switching frequency, efficiency of LLC resonant converter is still far better than PWM converters. To design the power stage of LLC resonant converter, DC analysis is performed with two methods: simulation and fundamental component simplification. Magnetic design is also discussed. The proposed integrated magnetic structure could achieve smaller volume, higher efficiency and easy manufacture. To make practical use of the topology, over load protection is a critical issue. Three methods to limit the stress under over load situation are discussed. With these methods, the converter could not only survive the over load condition, but also operate for long time under over load condition. Next small signal characteristic of the converter is investigated in order to design the feedback control. For resonant converter, state space average method is no longer valid. Two methods are used to investigate the small signal characteristic of LLC resonant converter: simulation and extended describing function method. Compare with test results, both methods could provide satisfactory results. To achieve both breadth and depth, two methods are both used to reveal the myth. With this information, compensator for feedback control could be designed. Test circuit of LLC resonant converter was developed for front end DC/DC application. With LLC topology, power density of 48W/in3 could be achieved compare with 13W/in3 for PWM converter. / Ph. D.

Small-signal stability is of great concern for distributed power systems with a large number of regulated power converters. These converters are constant-power loads (CPLs) exhibit a negative incremental input resistance within the output voltage regulation bandwidth. In the case of dc systems, design requirements for impedances that guarantee stability have been previously developed and are used in the design and specification of these systems. In terms of three-phase ac systems, a mathematical framework based on the generalized Nyquist stability criterion (GNC), reference frame theory, and multivariable control is set forth for stability assessment. However, this approach relies on the actual measurement of these impedances, which up to now has severely hindered its applicability. Addressing this shortcoming, this research investigates the small-signal stability of three-phase ac systems using measured d-q frame impedances. Prior to this research, negative incremental resistance is only found in CPLs as a results of output voltage regulation. In this research, negative incremental resistance is discovered in grid-tied inverters as a consequence of grid synchronization and current injection, where the bandwidth of the phase-locked loop determines the frequency range of the negative incremental resistance behavior, and the power rating of inverter determines the magnitude of the resistance. Prior to this research, grid synchronization stability issue and sub-synchronous oscillations between grid-tied inverter and its nearby rectifier under weak grid condition are reported and analyzed using characteristic equation of the system. This research proposes a more design oriented analysis approach based on the negative incremental resistance concept of grid-tied inverters. Grid synchronization stability issues are well explained under the framework of GNC. Although stability and its margin of ac system can be addressed using source and load impedances in d-q frame, method to specify the shape of load impedances to assure system stability is not reported. This research finds out that under unity power factor condition, three-phase ac system is decoupled. It can be simplified to two dc systems. Load impedances can be then specified to guarantee system stability and less conservative design. / Ph. D.

Les Systèmes électriques à Puissance Distribuée (SPD) sont utilisés dans de nombreux secteurs industriels. La sûreté de fonctionnement (SDF) et la continuité de service de ces SPDs sont aujourd'hui des préoccupations majeures. Une stratégie de gestion globale de l'énergie adaptée ainsi que leur stabilité sont des exigences fondamentales pour que ces systèmes puissent fonctionner correctement. La présence de charges déséquilibrées ainsi que les interactions entre convertisseurs dans ces systèmes peuvent conduire à l'instabilité du bus DC commun. Un des cas les plus connus en terme de cause d'instabilité est celui d'une charge "à puissance constante" (CPL). Par ailleurs, toute défaillance au niveau de l'interrupteur commandable du convertisseur peut provoquer de graves dysfonctionnements du système. Tout défaut non détecté et non compensé en temps réel peut rapidement mettre en danger l'ensemble du système de puissance. Par conséquent, la mise en oeuvre de méthodes efficaces et rapides de détection et de compensation de défaut est impérative. Afin d'assurer la continuité de service de ces systèmes. Dans ce mémoire, nous étudions la gestion de l'énergie, la stabilité et la continuité de service d'un DC-SPD. Après l'étude de la gestion de l'énergie et la stabilité du système, une méthode de stabilisation active décentralisée est proposée afin d'augmenter le domaine de stabilité du SPD et afin deéviter l'instabilité en présence de charges déséquilibrées. Par ailleurs, des méthodes de détection de défaut au niveau d'un interrupteur commandable, efficaces et très rapides, sont également proposées. Nous présentons également une topologie de convertisseur DC-DC à tolérance de pannes, intégrant un interrupteur redondant ; dans tous les cas de défaut (court-circuit ou circuit-ouvert), cette topologie doit permettre deassurer la continuité de service du système de puissance en mode normal. Les études théoriques ont été validées par la simulation et par des tests expérimentaux / Electric Distributed Power Systems (DPS) are used in many industrial sectors. Continuity of service of these systems as well as their reliability are now of the major concerned. Energy management and stability are fundamental requirements for these systems to operate normally. In these systems, load converters exhibit Constant Power Load (CPL) behavior tend to destabilize the system. The system stability also can be threatened by unbalanced loads connected to the common bus. Furthermore, the failure of the controllable switch of the converter can cause serious malfunctions of the system. Undetected and uncompensated fault in real time can quickly endanger the entire power system. Therefore, the implementation of effective and rapid fault detection methods and compensation is mandatory. In this thesis, we study the energy management, stability and continuity of service of a DC-DPS. After the study of energy management and system stability, an active decentralized stabilization method is proposed to increase the stability domain of the system and to avoid instability in the case of unbalanced loads. Furthermore, efficient and very rapid methods of fault detection for a controllable switch are also proposed. We have presented a fault tolerant topology with redundancy for a DC-DC converter, which must ensure continuity of service of the DPS in any fault conditions (open or short circuit). Theoretical studies have been validated by simulation and experimental tests

Power system generators are interconnected in a distributed network to allow sharing of power. If one of the generators cannot meet the power demand, spare power is diverted from neighbouring generators. However, this approach also allows for propagation of electric disturbances. An oscillation arising from a disturbance at a given generator site will affect the normal operation of neighbouring generators and might cause them to fail. Hours of production time will be lost in the time it takes to restart the power plant. If the disturbance is detected early, appropriate control measures can be applied to ensure system stability. The aim of this study is to improve existing algorithms that estimate the oscillation parameters from acquired generator data to detect potentially dangerous power system disturbances. When disturbances occur in power systems (due to load changes or faults), damped oscillations (or &quotmodes") are created. Modes which are heavily damped die out quickly and pose no threat to system stability. Lightly damped modes, by contrast, die out slowly and are more problematic. Of more concern still are &quotnegatively damped" modes which grow exponentially with time and can ultimately cause the power system to fail. Widespread blackouts are then possible. To avert power system failures it is necessary to monitor the damping of the oscillating modes. This thesis proposes a number of damping estimation algorithms for this task. If the damping is found to be very small or even negative, then additional damping needs to be introduced via appropriate control strategies. This thesis presents a number of new algorithms for estimating the damping of modal oscillations in power systems. The first of these algorithms uses multiple orthogonal sliding windows along with least-squares techniques to estimate the modal damping. This algorithm produces results which are superior to those of earlier sliding window algorithms (that use only one pair of sliding windows to estimate the damping). The second algorithm uses a different modification of the standard sliding window damping estimation algorithm - the algorithm exploits the fact that the Signal to Noise Ratio (SNR) within the Fourier transform of practical power system signals is typically constant across a wide frequency range. Accordingly, damping estimates are obtained at a range of frequencies and then averaged. The third algorithm applied to power system analysis is based on optimal estimation theory. It is computationally efficient and gives optimal accuracy, at least for modes which are well separated in frequency.