Dr. David Sehloff

I am working towards the Ph.D. degree with an interest in modeling and optimization of power systems with increasing penetration of renewable and distributed energy resources. I am particularly motivated to understand ways in which the planning and operations processes can quantify all the benefits and costs that non-traditional resources can bring to the system. My current focus is on developing tools which incorporate the steady state control of power, voltage, and frequency given by power electronic devices, along with analysis methods to incorporate stochastic phenomena.

Research

Low Frequency AC Transmission

Over the last century, power systems have evolved under certain paradigms which have guided their development. Throughout the world, nearly every large-scale power system has been built around the assumption of a standard grid frequency of 50 or 60 Hz. The choices of these frequencies came from tradeoffs involving a number of factors, many of which were quite salient to the systems of a century ago but have since become less relevant.

The capabilities of contemporary power electronics remove the necessity of having the same frequency throughout a system and even the need for a fixed, standard frequency. This has positive implications for the performance of the system. For example, significant advantages for power flow can be gained when the frequency is lowered. Understanding whether this type of configuration makes sense, either to upgrade an existing network or for new construction, requires the development of new analysis tools.

The same tools used for planning and operations need to be extended for this freedom to treat the frequency as a variable. The frequency is considered a variable in the modeling, and the validity of assumptions relying on 50 or 60 Hz frequency must be validated for the new potential frequencies. From this foundation, tools for power flow, optimal power flow, and security constrained optimal power flow will enable planners to include a full evaluation of the system-level impacts of these upgrades.

By formulating and solving the optimal power flow problem with frequency as a variable, we see that in many cases, the best performance of a constrained transmission system is found at intermediate frequencies, lower than 50 Hz but higher than DC. This results from the interaction of several transmission constraints which change with frequency.

This work is supported by and in collaboration with the New York Power Authority.

Adoption of Distributed Energy Resources and Rate Design in Distribution Grids

Integration of large amounts of distributed energy resources into a distribution grid requires a quantitative understanding of the impacts of these resources on the grid. Because several significant sources of uncertainty affect these resources, multistage stochastic tools are needed for power flow analysis in a distribution system. In this work, we introduce a multi-stage probabilistic load flow algorithm and use it to analyze the effects of utility rate design decisions on the distribution system performance, where the decisions made by individual customers of whether to adopt certain recommended resources are considered uncertain with a known probability distribution. This can give general insights into utility rate design and provides a tool for quantitative analysis of a specific system under a particular context.

Grid Optimization Competition

A major need in power system operations is a reliable, efficient algorithm for the solution of the AC optimal power flow problem, particularly the security constrained problem with N-1 contingencies. This problem, which ensures that the system can remain secure under any single outage in the large number of possibilities considered, is a large scale, nonlinear, nonconvex optimization problem. As a member of the Lawrence Berkeley Laboratory team supported by ARPA-E for Challenge 1, I worked to develop and test algorithms to approximate and solve the problem efficiently, and I led the development of the final codebase for the team.

Publications

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