
NSF Org: |
ECCS Division of Electrical, Communications and Cyber Systems |
Recipient: |
|
Initial Amendment Date: | June 7, 2016 |
Latest Amendment Date: | January 22, 2020 |
Award Number: | 1608929 |
Award Instrument: | Standard Grant |
Program Manager: |
Lawrence Goldberg
ECCS Division of Electrical, Communications and Cyber Systems ENG Directorate for Engineering |
Start Date: | June 1, 2016 |
End Date: | May 31, 2020 (Estimated) |
Total Intended Award Amount: | $239,599.00 |
Total Awarded Amount to Date: | $268,965.00 |
Funds Obligated to Date: |
FY 2019 = $29,366.00 |
History of Investigator: |
|
Recipient Sponsored Research Office: |
2200 W MAIN ST DURHAM NC US 27705-4640 (919)684-3030 |
Sponsor Congressional District: |
|
Primary Place of Performance: |
2200 W. Main St, Suite 710 Durham NC US 27705-4010 |
Primary Place of
Performance Congressional District: |
|
Unique Entity Identifier (UEI): |
|
Parent UEI: |
|
NSF Program(s): |
GOALI-Grnt Opp Acad Lia wIndus, EPCN-Energy-Power-Ctrl-Netwrks |
Primary Program Source: |
01001920DB NSF RESEARCH & RELATED ACTIVIT |
Program Reference Code(s): |
|
Program Element Code(s): |
|
Award Agency Code: | 4900 |
Fund Agency Code: | 4900 |
Assistance Listing Number(s): | 47.041 |
ABSTRACT
Rechargeable-battery systems are critical to two technologies that will help reduce the consumption of fossil fuels: electrically-powered transportation systems and energy storage systems for the grid. Despite great improvements in battery cell performance, battery integration into systems still faces significant challenges. Existing solutions are typically highly integrated with the target application, and cannot be repurposed. The systems are often not scalable, and the failure of a single battery cell can cause the entire system to fail. In addition, the power electronics of such systems is optimized for the nominal load, not for partial load, where the system typically operates. This work explores a radically new approach to designing energy storage and energy conversion systems by modularizing and integrating the battery with the power electronics to provide multiple functions using the same semiconductor chip area. The proposed battery technology will use a new multilevel inverter topology that allows dynamically reconfigurable series and parallel connectivity: the modular multilevel series-parallel converter (MMSPC). Modular design of identical sub-systems will enable the same modules to be used in multiple applications, making use of economies of scale to reduce system cost. In electric vehicles, the proposed system can replace hard-wired battery packs with a flexible, dynamically reconfigurable AC battery and replace multiple power electronics units, such as the drive inverter, battery charger, and battery balancing circuits, to provide the output directly from the AC battery. For grid energy storage, the proposed technology enables repurposing modules from various applications, such as electric vehicles, incorporation of cells of different capacity or age into one system, high output quality with substantially reduced or eliminated magnetic components, rapid dynamic response, and easy scaling of the storage and power converter systems by simple addition of AC battery modules.
To leverage the advantages of MMSPC, efficient control strategies have to be developed to optimize performance while minimizing system complexity and cost. The control of modular multilevel converters (MMCs) presents both challenges and opportunities associated with the large number of possible switch states. The MMSPC degrees of freedom are even more due to the additional parallel state, which allows widely flexible series-parallel configuration of the circuit, amplifying the need for a coherent control strategy. For instance, in both MMC and MMSPC the same output voltage can be achieved with a multitude of module configurations, providing the opportunity to optimize the switch states based on various additional constraints and objectives such as module balancing, efficiency, output quality, electromagnetic emissions, and switch and storage-element stress. Existing control approaches, however, do not fully exploit this opportunity as they typically reduce the number of objectives and treat the various constraints and objectives independently. Critically, established strategies are not designed to utilize parallel connectivity, precluding exploitation of the MMSPC advantages. Addressing these limitations, we propose to develop a real-time predictive multi-objective optimization framework that systematically unifies the treatment of multiple system constraints and objectives, and overcomes the exponential growth of degrees of freedom with system size and prediction horizon. This control framework will be applicable to both MMC and MMSPC, and will consider additional topology variations within each of these converter families. The advantages of the novel MMSPC topology and control strategy will be demonstrated with the development of a modular AC battery that incorporates multiple battery units, battery management, and inverter functionality for applications such as energy storage systems and electric vehicle drive trains. This innovative concept will improve lifetime, efficiency, and cost of battery systems, and is practical only when the capabilities of the MMSPC and the associated control are leveraged.
PUBLICATIONS PRODUCED AS A RESULT OF THIS RESEARCH
Note:
When clicking on a Digital Object Identifier (DOI) number, you will be taken to an external
site maintained by the publisher. Some full text articles may not yet be available without a
charge during the embargo (administrative interval).
Some links on this page may take you to non-federal websites. Their policies may differ from
this site.
PROJECT OUTCOMES REPORT
Disclaimer
This Project Outcomes Report for the General Public is displayed verbatim as submitted by the Principal Investigator (PI) for this award. Any opinions, findings, and conclusions or recommendations expressed in this Report are those of the PI and do not necessarily reflect the views of the National Science Foundation; NSF has not approved or endorsed its content.
This project developed an entirely new electronic circuit technology. Power electronics is needed in practically every modern device, ranging from computer power supplies, cell-phone chargers, and LED lamps to solar as well as wind grid converters and electric vehicle drive trains.
In contrast to more conventional converters, this circuit technology allows highly flexible conversion of electrical power, e.g., from direct current (DC) to alternating current (AC) with high accuracy. However, technologically notably more interesting is the circuit?s ability to form previously impossible devices, such as dynamically reconfigurable batteries. Such reconfigurable batteries can overcome major issues of current lithium-ion batteries, namely their large parameter spread so that the weakest cell limits the entire pack in terms of power, ageing, and capacitance. Instead, the reconfigurable battery based on this circuit can load each cell exactly to its potential. Furthermore, instead of a DC voltage that also varies up to a factor of two from full to empty, the circuit can generate any desired voltage shape and amplitude within a certain range at any time.
In contrast to previous suggestions with a similar vision, the circuit consequently breaks higher voltage and power of the output into smaller voltage and current units to exclusively allow the use of low-voltage components in the units and distribute power almost freely. Topologically, the studied circuit is a hybrid of modular multilevel converters and switched-capacitor converters, two of the major inventions in power electronics. The former enabled highly flexible and compact DC power transmission as installed on offshore wind parks or to provide the supply of cities across barriers such as the trans-bay line in San Francisco and units to stabilize our modern power grids. The latter is the basis that enabled our modern cell phones and powerful computer processors. However, these technologies with their very specific features and advantages developed in a very separate way and did not appear to share a common ground. However, the team discovered a circuit topology that indeed unites both, can use the operation principles of both, and inherit their advantages. Still, the solution does not need to give up the major advantage of exclusively low-power components, which operate together to manage large overall powers. The circuit is both multilevel converter and switched-capacitor converter and thus allows very accurate control of its output.
In addition, the project developed control methods to manage the high flexibility of the circuit, i.e., the many options a controller has to activate transistors inside to achieve similar output but with substantially different efficiency and stress on the components as well as ageing potential. Particularly in combination with batteries, control methods as developed during this project
The major outcomes of this project are (1) an entire class of highly flexible converter circuits and rules to form and size such circuits; (2) control methods to deal with the high flexibility, i.e., the many alternatives a controller has for its next moves to systematically achieve additional goals, such as to increase efficiency, to maximize the overall available capacitance in case of batteries, allow low-frequency output (which conventional modular converters cannot provide), or reduce degrading ripple load on battery cells; (3) a high-power demonstrator with 3x 100 V and 350 A to feed a an electric drive train or convert DC to AC power down to 0 Hz.
The developed technology has specific applications. The circuit opened motor drives for modular multilevel converters, which are considered the most promising solution for large drives and their problem of degradation when connected to conventional converters but which previously could not provide the low-frequency output required for start-up or low speeds. In addition, the merger of the circuit with batteries could revolutionize batteries in general to turn them from a relatively passive and uncontrollable element to a highly flexible and adaptive power source with higher performance per weight. Furthermore, the circuit turned out to be the first solution to two older but open problems in medical technology. The development of two corresponding prototype systems is under way and will enable human studies supported by the National Institutes of Health (NIH) subsequently.
The results of this project have been extensively published in scientific journals so that further work by others can build upon it and drive technological progress.
Last Modified: 09/27/2020
Modified by: Angel V Peterchev
Please report errors in award information by writing to: awardsearch@nsf.gov.