In the past, my group and I have focused on research areas that can be categorized as follows, with the corresponding publications and patents listed separately on this website:
- Power System Applications: Superconducting Magnetic Energy Storage; Effect of Geo-magnetically Induced Currents (GIC) in power systems, STATCOMs, EMTP-based Modeling and capability to include hysteresis losses in transformers
- Power Quality: Active Filters; Interface to draw sinusoidal grid-side currents at unity power factor
- Design and Control of Electric Machines; Efficiency Improvements
- Soft-Switching DC-DC Converters and DC-AC Inverters
- Power electronic converters for interfacing of Wind, PVs, EVs and Plug-in Hybrids
To carry out research in the past and at present, funding from NSF, NASA, The United States Navy (ONR), DOE, EPRI and other private companies is gratefully acknowledged. The stalwart support all through the years has been by the University of Minnesota Center for Electric Energy (UMCEE), established by my mentor Prof. Vernon D. Albertson in 1981, with me as a junior partner. The present Director is my colleague Prof. Bruce Wollenberg. UMCEE consists of the following seven regional utilities: Xcel Energy, Minnesota Power, Great River Energy (GRE), Ottertail Power, Dairyland Cooperative and SMMPA in Rochester, MN.
Recent Research Focus
Listed below are the areas that our group is focusing at present. However, we are flexible in pursuing any other meaningful research areas related to those under present consideration.
1. Open-ended Drives supplied through Matrix Converters:
As the diagram shows it in its rudimentary form, the focus of this research is to supply ac motors and generators from both sides by matrix converters, with the following objectives: 1) elimination of bulky and unreliable storage capacitors, particularly problematic at high temperatures associated with utilizing SiC devices, so as to integrate power electronics with electric machines, and 2) elimination of stray currents that can degrade reliability due to bearing currents by avoiding the switching of common-mode voltages.
Applications: Motors and Generators in Naval Ships and Submarines, wind generators
Ned Mohan K. Mohapatra
Students/Post-docs: Dr. Krushna Mohapatra (post-doc), Satish Thuta (PhD 2007), Ranjan Gupta (PhD 2010), Rashmi Prasad (PhD 2011), Apurva Somani (expected PhD May 2012)
Funding: UMN Innovation Grant, U.S. Navy (Office of Naval Research)
Student Recognition: R.K. Gupta and A. Somani chosen as the recipients of the 2011 Student Best Paper Award, the IEEE- Industrial Electronics Society Transactions. R.K. Gupta, K.K. Mohapatra, A. Somani, and N. Mohan, "Direct-Matrix-Converter-Based Drive for a Three-Phase Open-End-Winding AC Machine With Advanced Features," Trans. IE vol.57, no.12, pp.4032-4042, Dec. 2010.
2. Power-Electronic Based Transformers
As the picture from Los Alamos shows, high-frequency transformers can be two-orders of magnitude smaller in size and weight. These can be used to replace line-frequency transformers by using power electronic converters, as shown in its rudimentary form .
Applications: Naval Ships and Submarines, wind generators, interface with bi-directional power flow for EVs and plug-in HEVs, photovoltaic interface, power distribution
Publication #: 2011/0007534
Students/Post-docs: Dr. Amod Umarikar, Dr. Krushna Mohapatra (post-doc), Ranjan Gupta (PhD 2010), Nathan Wiese (PhD 2011), Shabari Nath (expected PhD June 2011), Kaushik Basu (expected PhD August 2012), Gysler Castelino (expected PhD Dec 2012)
Funding: U.S. Navy (Office of Naval Research)
3. An Industry/Academe Consortium for Achieving 20% Wind by 2030 through Cutting-Edge Research and Workforce Training
As the picture during its construction shows, through an approximately 8 M$ grant (PI: Prof. Fotis Sotiropoulos) from DOE, our university has installed a utility-scale 2.5 MW wind turbine, close to the UMN campus. It is very-well instrumented and is providing measurements at 1 Hz and 20 Hz rates. This is a living laboratory for interdisciplinary research. One of the research projects is on generation, which is a combination of our research on power-electronics based transformers and conventional two-level inverters in an open-ended generator arrangement to eliminate bearing currents. Education and outreach are other important aspects of this project.
Students: Gysler Castelino (expected PhD Dec 2012), Rohit Baranwal (passed PhD Qualifying Exam)
4. Storage for Further Integration of Renewable Energy Into the Grid
(a) A high-temperature sodium-sulfur battery: Xcel Energy has spent several million dollars for installing a 1 MW, 7.2 MWh high-temperature sodium-sulfur battery to study the feasibility of battery storage to further the integration of wind into power systems. This battery-storage is very-well instrumented and it is a living laboratory where charge/discharge rates can be controlled. As a co-PI, our research group was involved in its initial installation discussions and sensors and then using the actual data, and combing it with the historical meteorological data to determine the optimum amount of storage as a percentage penetration of renewables and economic feasibility on nodes with large LMP fluctuations.
Student: Saurabh Tewari (MS 2011; passed PhD qualifying exam)
- Tewari, S.; Geyer, C.J.; Mohan, N.; , "A Statistical Model for Wind Power Forecast Error and its Application to the Estimation of Penalties in Liberalized Markets," Power Systems, IEEE Transactions on, vol.26, no.4, pp.2031-2039, Nov. 2011
- Tewari, Saurabh; Mohan, N. "Value of NAS Energy Storage toward integrating Wind: Results from the Wind to Battery Project", Submitted for review to the IEEE Transactions on Power Systems.
Funding: XCEL Energy and IREE (UMN).
(b) Flywheel-based Energy Storage Modules for Distributed Storage: The goal of this research is to develop modular storage for the distribution grid based on flywheel technology. The flywheel is to be magnetically suspended, located in a vacuum chamber, and operated at high speed. For example, a module may be rated at 2.5 KW, store 10 kW-hr, and spin at 36,000 RPM. Novel motor/generator design is a key requirement of the project. For this purpose, bearingless homopolar ac machines are being investigated.
Student: Eric Severson (passed PhD qualifying exam)
- E. Severson, R. Nilssen, T. Undeland, N. Mohan, "Investigation of dual purpose winding approaches for bearingless ac homopolar motors," IEEE IPEC, May 2014, Hiroshima, Japan, Accepted
- E. Severson, R. Nilssen, T. Undelan, N. Mohan, "Outer-rotor ac homopolar motors for flywheel energy storage," IET PEMD, April 2014, Manchester, UK, Accepted
- E. Severson, R. Nilssen, T. Undeland, N. Mohan, "Suspension force model for bearingless ac homopolar machines designed for flywheel energy storage," IEEE GCC, pp. 274-279, November 2013, Doha, Qatar
- E. Severson, A. Rokke, R. Nilssen, T. Undeland, N. Mohan, "Design and measurement of a passive thrust magnetic bearing for a bearingless motor," IEEE IECON, pp. 2720-2725, November 2013, Vienna, Austria
- E. Severson, R. Nilssen, T. Undeland, N. Mohan, "Experimental results and 3D finite element analysis of the ac homopolar motor," MMM/IEEE Intermag, Chicago, IL, January 2013, Presented
- E. Severson, R. Nilssen, T. Undeland, N. Mohan, "Analysis of the bearingless ac homopolar motor," IEEE ICEM 2012, pp 568-574, Marseille, France, September 2012.
Funding: Student, Eric Severson, is supported by NSF-Graduate Research Fellowship Program and DoD’s NDSEG Fellowship; project is in collaboration with a grant from NTNU, Trondheim, Norway.
5. Research in Educational Pedagogy :
With NSF funding my co-PIs (Prof. Tamara Moore at UMN and Prof. Allison Kipple at the Northern Arizona University) and I are doing collaborative research on an innovative instructional strategy for widespread implementation of electric energy systems curriculum, as a model in STEM education. The ultimate goal of this project is to develop a forward-looking curriculum that can be widely implemented and thus results in a large number of graduates with the world-class education to tackle immediate and critical societal challenges in the area of Electric Energy systems. It has resulted in a recently launched effort called Consortium of Universities for Sustainable Power (CUSP™) which has the following website: www.cusp.umn.edu.