Seminars and Defenses

All are welcome and encouraged to attend the seminars and defenses.

Jan. 15, 4PM, EPH 112
Zhi-Quan (Tom) Luo • Research Seminar
Analysis of Alternating Direction Method of Multipliers for Nonconvex Problems
A popular approach to solve large scale optimization problems involving big data is by the Alternating Direction Method of Multipliers (ADMM). The existing convergence analysis of this algorithm is limited mostly to the convex case. In this talk, we will present some recent work on the analysis of ADMM for the nonconvex case and discuss some open questions.

ZHI-QUAN TOM LUO received his B.Sc, Applied Mathematics, from Peking University in 1984 and PhD in Operations Research from MIT in 1989. He was with the McMaster University, Canada, from 1989 to 2003, where he served as the Head of the ECE Department and held a Canada Research Chair in Information Processing. He has been with the ECE Department at the University of Minnesota (Twin Cities), since 2003. He is Vice President (Academic) and Professor of School of Science and Engineering, the Chinese University of Hong Kong (Shenzhen) (2014-present). He is also concurrently serving as the founding director of the Shenzhen Research Institute of Big Data. His research interests lie in optimization algorithms for signal processing, data analytics and digital communication.
Jan. 10, 2 PM, ENG460
Maryam Gholizadeh-Ansari • MASC thesis defense
Deep learning for Low-Dose CT Noise Removal Using Dilated Convolution and Perceptual loss
Low-dose computed tomography has been recommended to reduce the radiation risks of CT scans for patients. However, the reconstructed CT image will be considerably degraded because of photon starvation. Both traditional noise removal techniques and neural networks have been used to enhance the quality of low-dose CT images. In this study, a deep neural network is proposed to mitigate this problem. The network em ploys dilated convolution, batch normalization, and residual learning. Moreover, a non trainable edge detection layer is proposed helping to produce sharper edges in the output image without introducing additional complexity. This network is optimized by a combination of mean-square error and perceptual loss to preserve textural details in the CT image that are critical for diagnosis. This objective function solves the over-smoothing problem and grid-like artifacts caused by per-pixel loss and perceptual loss, respectively. The experiments demonstrate the effects of each modification to the network and confirm that the proposed network achieves better performance relative to the state-of-the-art methods.
Jan. 8, 10AM, ENG460
Saman Alaeddini • MASC thesis defense
Holistic approach to achieve wide area protection coordination
The electric power transmission network of today is undergoing significant changes in terms of the operational requirements, connected distributed energy resources technologies, and regulatory requirements. In conjunction with an aging infrastructure, these changes have presented new challenges to utilities in their fundamental mission of providing reliable electrical power to the customers. Thus, protection systems must overcome additional challenges towards safe and reliable operation of the power system. Increased investigation of protection system performance is therefore needed to ensure proper coordination of protective relays. However, the complex and integrated nature of the modern protection and control systems call for more sophisticated modeling and study tools for the simulation and analysis of both the dynamics of the interconnected transmission systems and interactions among numerous sets of intelligent electronic devices. Although the protection technology designed for transmission systems is mature, coordination of devices is still a major challenge. This thesis presents a holistic approach to conducting wide-area protection coordination studies through the use of a practical automation-assisted methodology. The wide area protection coordination solution covers process and data management considerations. It also provides a framework workflow for the execution and review of coordination studies, as well as processing and documentation of results to support reliability improvements. The fundamental concept behind the proposed approach is the utilization of software-based automation in a number of key tasks. Firstly, the execution of large-scale protection system coordination studies can be largely automated through utilization of specialized scripts running within short circuit simulation software packages. Secondly, the vast amounts of data inherent in the protection system coordination study results are processed in a manner that assists protection engineers in the identification and resolution of coordination issues. Finally, user friendly automated study summaries are generated that can be used as a record of protection setting recommendations. The effectiveness of the proposed solution is demonstrated through simulations conducted in the CAPE software environment for short circuit studies.
Jan. 7, 10AM, ENG460
Jahan Afsharian • PHD thesis final defense
High power density matrix converter based power supplies for telecom and datacenter applications
With the fast development of information technology (IT) industry, the demand and market volume for off-line power supplies keeps increasing, especially those for telecommunication, computer server and datacenter. The total power consumption of today's data centers is = becoming noticeable. In 2014, data centers in the U.S. consumed an estimated 70 billion kWh, representing about 1.8% of total U.S. electricity consumption. Moreover, with the increase in cloud computing and big data, energy use of data centers is expected to continue rapidly increasing in the near future. Generally, the power supply (PSU) for power distribution system (PDS) in datacenter and telecom are the standard two-stage approach. An off-line PSU normally consists of power factor correction (PFC) circuit and isolated dc-dc converter. The front-end PSU needs to meet several rigid requirements of IT equipment, such as input to output isolation, tight output voltage regulation, high-efficiency, high-power-density and n+1 parallel operation. Besides these indispensable requirements, power quality is a major concern and stringent international requirements, such as the IEC 61000-3-2, is enforced to limit the harmonic currents drawn by the off-line equipment. The PSU has to meet the requirements for abnormal input operation such as loss of one phase in three-phase operation, voltage sag, unbalanced input voltage and surge voltage. In general, the two-stage power conversion has demonstrated excellent performance and high reliability, since the design can be optimized for each stage. In order to fulfill future requirements for the PDS in datacenter and telecom applications, it is therefore of great importance to identify new ways to develop systems with higher efficiency, power density, reliability and lower cost. A very promising and fundamentally different approach, in order to fulfill the future demands for PDS in datacenter and telecom, is the development of single-stage converter. The development of single-stage matrix-type converter creates new degrees of freedom regarding e.g. simplified rectifier racks in telecom and datacenter. This provides tangible benefits in the form of space saving, and better airflow for power unit in rectifier racks.
Dec. 3, 10AM
Amr Adel Fathy Mohamed • PHD internal exam
Line-wise power balance equations and applications
Optimal power flow (OPF) is the optimization of a chosen objective function by determining the best values of control variables while satisfying a set of equality and inequality constraints. Even though commercial OPF algorithms are robust and efficient, they still cannot guarantee a global optimum. The US Federal Energy Regulatory Commission estimates that the best commercial OPF solvers are off by 10%, precipitating an economic loss of US $400 billion per year worldwide. In addition, the continuous necessity to ensure voltage stability of power systems while operating at the minimum cost necessitates incorporation of voltage stability constraints into optimal power flow formulations. For these reasons and given the nonlinear and nonconvex characteristics of the optimization problem, there is significant technical and economic impetus whereby OPF remains a major research focus. This thesis aims to (1) develop a new set of power balance equations yielding faster power flow (PF) algorithms with better solution space that are the best suited for OPF applications, (2) build new OPF formulations using this new set of power balance equations, and (3) incorporate voltage stability constraints into the newly developed OPF formulation. The genesis of the new set of power balance equations stems from the fact that power of a constant impedance load is proportional to the square of voltage magnitude. Using square of voltage magnitude in conjunction with angles of bus voltage phasors, a set of line-wise power balance equations is developed, both in polar and rectangular forms. The solution algorithm of these two formulations is developed using Newton-Raphson (NR) technique. All developed methods are tested on 6-, 14-, 57- and 118-bus IEEE systems, a 582-bus real system, a 2383-bus Polish power system, and a 9241-bus PEGASE system. Tests show that the developed line-wise power flow (LWPF) is accurate, provides monotonic convergence, and scales well for large systems, while using sparse matrices. Studies also show that the newly proposed LWPF methods are up to twice and thrice faster for polar and rectangular forms respectively, when compared with conventional bus-wise power flow (BWPF) methods that use bus-wise power balance equations. Numerical analysis of the Jacobians of BWPF and LWPF methods shows that the number of calculations required for the LWPF method is much lower, resulting in the higher speed. Another significant benefit of the polar form LWPF method is the ability to directly identify the set of critical lines that connect busses that are the most susceptible to Voltage collapse (VC). Based on the polar form of a line-wise set of power balance equations, a novel line-wise optimal power flow (LWOPF) is developed. LWOPF is linearized and solved using successive linear programming. Due to the better solution space modeled by LWPF equations, the optimal solution yielded by the LWOPF is consistently better than that computed using bus-wise OPF. The polar form of LWOPF is extended to include voltage stability constraints and implemented considering both linear and nonlinear optimization techniques. It demonstrates improved performance in achieving lower cost optimal solutions with better voltage-stable states.