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- Bessman, Alexander, et al.
(författare)
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Aging effects of AC harmonics on lithium-ion cells
- 2019
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Ingår i: Journal of Energy Storage. - : Elsevier. - 2352-152X .- 2352-1538. ; 21, s. 741-749
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Tidskriftsartikel (refereegranskat)abstract
- With the vehicle industry poised to take the step into the era of electric vehicles, concerns have been raised that AC harmonics arising from switching of power electronics and harmonics in electric machinery may damage the battery. In light of this, we have studied the effect of several different frequencies on the aging of 28 Ah commercial NMC/graphite prismatic lithium-ion battery cells. The tested frequencies are 1 Hz, 100 Hz, and 1 kHz, all with a peak amplitude of 21 A. Both the effect on cycled cells and calendar aged cells is tested. The cycled cells are cycled at a rate of 1C:1C, i.e., 28 A during both charging and discharging, with the exception of a period of constant voltage at the end of every charge. After running for one year, the cycled cells have completed approximately 2000 cycles. The cells are characterized periodically to follow how their capacities and power capabilities evolve. After completion of the test about 80% of the initial capacity remained and no increase in resistance was observed. No negative effect on either capacity fade or power fade is observed in this study, and no difference in aging mechanism is detected when using non-invasive electrochemical methods of post mortem investigation.
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| 3. |
- Bessman, Alexander, 1989-, et al.
(författare)
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Challenging Sinusoidal Ripple-Current Charging of Lithium-Ion Batteries
- 2018
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Ingår i: IEEE Transactions on Industrial Electronics. - : IEEE Press. - 0278-0046 .- 1557-9948. ; 65:6, s. 4750-4757
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Tidskriftsartikel (refereegranskat)abstract
- Sinusoidal ripple-current charging has previously been reported to increase both charging efficiency and energy efficiency and decrease charging time when used to charge lithium-ion battery cells. In this paper, we show that no such effect exists in lithium-ion battery cells, based on an experimental study of large-size prismatic cells. Additionally, we use a physics-based model to show that no such effect should exist, based on the underlying electrochemical principles.
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| 4. |
- Bessman, Alexander
(författare)
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Interactions between battery and power electronics in an electric vehicle drivetrain
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The electric machine and power electronics in electric and hybrid electric vehicles inevitably cause AC harmonics on the vehicle's DC-link. These harmonics can be partially filtered out by large capacitors, which today are overdimensioned in order to protect the vehicle's battery pack. This is done as a precaution, since it is not known whether ripple-current has any harmful effect on Li-ion cells.We have measured and analyzed the ripple-current present in a hybrid electric bus, and found that a majority of the power was carried by frequencies in the range 100~Hz to 1~kHz. The single most energetic harmonic in this particular vehicle is believed to have been caused by a misaligned resolver in the motor.We have also designed and built an advanced experimental set-up in order to study the effect of ripple-current on Li-ion cells in the lab. The set-up can cycle up to 16 cells simultaneously, with currents of up to 50~A including a superimposed AC signal with a frequency of up to 2~kHz. The cells' temperatures are controlled by means of a climate chamber. The set-up also includes a sophisticated safety system which automatically acts to prevent dangerous situations before they arise.Using this set-up we tested whether superimposing AC with a specific frequency improves the charging performance of Li-ion cells. Statistical analysis found no improvement over regular DC cycling, and a physics-based model explains the experimental findings.We have also investigated whether ripple-current accelerates the aging of Li-ion cells. Twelve cells were either calendar or cycle aged for one year, with some cells being exposed to superimposed AC with a frequency of 1~Hz, 100~Hz, or 1~kHz. No effect was observed on any of capacity fade, power fade, or aging mechanism.Finally we also tested whether it is possible to heat Li-ion cells from low temperatures using only AC. We propose a method for AC heating of Li-ion cells, and open the discussion for generalizing the technique to larger battery packs.In conclusion, ripple-current has negligible effect on Li-ion cells, except for heating them slightly.
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| 5. |
- Bessman, Alexander, et al.
(författare)
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Investigating the aging effect of current ripple on lithium-ion cells
- 2015
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Ingår i: ECS Transactions. - : Electrochemical Society. - 1938-6737. - 9781607685395 ; , s. 101-106
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Konferensbidrag (refereegranskat)abstract
- We have built an experimental setup which exposes twelve cells to a well-defined ripple current. It consists of a system for cycling high capacity cells in parallel with a triangular current waveform superimposed on top of the direct current. The frequency of the waveform is variable up to 50 Hz, and the sum of the DC and AC components can have a magnitude of -40 A to 40 A. Current is measured over a 500 μω shunt resistor. The voltage and current of each cell is read simultaneously at a sample rate up to 4 MS/s, allowing for precise impedance measurements even for high frequency harmonics. The cells are cycled at 40 °C. The experiment has been designed to eliminate indirect effects of the AC harmonics as far as possible. This system is being used to test whether or not AC harmonics affect Li-ion aging.
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| 9. |
- Soares, Rudi, et al.
(författare)
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An Experimental Setup with Alternating Current Capability for Evaluating Large Lithium-Ion Battery Cells
- 2018
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Ingår i: Batteries-Basel. - : MDPI. - 2313-0105. ; 4:3
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Tidskriftsartikel (refereegranskat)abstract
- In the majority of applications using lithium-ion batteries, batteries are exposed to some harmonic content apart from the main charging/discharging current. The understanding of the effects that alternating currents have on batteries requires specific characterization methods and accurate measurement equipment. The lack of commercial battery testers with high alternating current capability simultaneously to the ability of operating at frequencies above 200 Hz, led to the design of the presented experimental setup. Additionally, the experimental setup expands the state-of-the-art of lithium-ion batteries testers by incorporating relevant lithium-ion battery cell characterization routines, namely hybrid pulse power current, incremental capacity analysis and galvanic intermittent titration technique. In this paper the hardware and the measurement capabilities of the experimental setup are presented. Moreover, the measurements errors due to the setup’s instruments were analysed to ensure lithium-ion batteries cell characterization quality. Finally, this paper presents preliminary results of capacity fade tests where 28 Ah cells were cycled with and without the injection of 21 A alternating at 1 kHz. Up to 300 cycles, no significant fade in cell capacity may be measured, meaning that alternating currents may not be as harmful for lithium-ion batteries as considered so far.
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| 10. |
- Soares, Rúdi, 1984-
(författare)
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Analysis and Prediction of the Harmonic Content in the Battery Currentof a Commercial Hybrid-Electric Bus
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Ingår i: IEEE Transactions on Transportation Electrification.
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents a comparison of the harmoniccontent in the battery current in two, commercialhybrid electric vehicles (HEVs) (intercity passenger buses)when operated in realistic drive scenarios. These harmonicscan contribute to issues related to electromagnetic compatibilityand indirectly accelerate the aging of the battery dueto elevated cell temperatures caused by associated ohmiclosses. A key finding is that low-frequency harmonics (upto approximately 130 Hz) attributed to resolver eccentricityand non-ideal effects in the voltage-source inverter (VSI) (upto approximately 260 Hz) were significant in terms of magnitudes.Also, the variation between the two HEVs (in termsof current magnitude) were substantial for these harmonics.This is an important observation since it demonstratesthat significant, low-frequency harmonics can be presentin the battery current and that modeling and collectingexperimental data from a single corresponding vehicle maynot sufficiently represent the harmonic content in the batterycurrent for a fleet of vehicles.
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