| 1. |
- Josefsson, Oskar, 1985, et al.
(författare)
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Assessment of a Multilevel Converter for a PHEV charge and traction application
- 2010
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Ingår i: XIX International Conference on Electrical Machines (ICEM), 2010, Rome, 6-8 Sept. 2010. - 9781424441747
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Konferensbidrag (refereegranskat)abstract
- With the Plug in Hybrid Electric Vehicle (PHEV) the introduction of a charger has to be done. A standalone onboard charger will increase both weight and cost of the vehicle. A better option is the integration of the charging function into the already existing propulsion converter. The aim of this paper is to assess the multilevel converter as an integrated vehicle charge and propulsion converter. A comparison between conventional converter technology and multilevel converter technology is made both on component level and system level. The investigation, based on calculations, simulations and measurements, points to some features that can; increase the efficiency of the total system; increase the life time of the energy storage; and increase the utilization of the energy storage. However, the investigation also points to features that can increase the cost and complexity of the system and reduce efficiency in certain operation points.
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| 2. |
- Josefsson, Oskar, 1985
(författare)
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Energy Efficiency Comparison Between Two-level and Multilevel Inverters for Electric Vehicle Applications
- 2013
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In order to contribute to the development of energy and cost efficient electric vehicles, a thorough analysis of two different electric converter topologies is performed, considering different drive cycles and different control strategies. In the electric vehicles available on the market today, a high voltage (200−400 V ) battery pack composed of several battery modules is connected to one or more inverters which create AC voltages to the electric propulsion machines. This thesis analyses the use of a modular battery-inverter concept, the cascaded multilevel inverter. Here, the battery modules have one inverter for each battery module, the inverters are then connected in series and controlled in order to create the AC voltages for the electric machines. The simulation results shows that this concept lowers the inverter losses, mainly due to the possibility to use MOSFETs instead of IGBTs. The losses in the battery are on the other hand increased. If there was a possibility to filter out reactive power and harmonics from the battery (using input capacitors for each inverter), the drive train with the multilevel inverter will have lower losses than the two-level inverter for all the analysed driving cycles. If such filter capacitors can not be used, it is not beneficial to use the multilevel inverter for high speed driving cycles, such as the US06. For the more moderate new European driving cycle, the accumulated drive cycle losses in the battery and inverter are reduced by 25 % when using the multilevel inverter, even without filter capacitors, compared to the two-level inverter. Furthermore, when using infinitely large supporting capacitors in parallel to the battery modules, the loss reduction for the inverter and the battery becomes 72 % compared to the two-level inverter.The multilevel inverter is able to control from which battery modules the energy is taken from, therefore the battery capacity is no longer limited by the weakest battery module. If one of the modules is damaged and the available energy is lower, the inverter can be controlled to utilize the remaining energy in the battery pack so the effect of the faulty module is not so severe. When using the propulsion inverter as a charger, the multilevel inverter also shows an increase in efficiency compared to the two-level inverter.
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| 3. |
- Josefsson, Oskar, 1985, et al.
(författare)
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Evaluation and comparison of a two-level and a multilevel inverter for an EV using a modulized battery topology
- 2012
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Ingår i: IECON Proceedings (Industrial Electronics Conference). - 2162-4704 .- 2577-1647. - 9781467324199 ; , s. 2949 - 2956
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Konferensbidrag (refereegranskat)abstract
- This paper analytically evaluates when it is suitable to use a multilevel inverter in an electrified vehicle. The multilevel inverter is compared to a classical two level inverter for different operation points and for different drive cycles.Reliable models of the components which build up the inverter are needed in order to be able to calculate the losses. Analytical models for the losses are developed to be able to compare the two inverters. Since the two inverters utilizes the battery in different ways the losses in the battery is also considered.It is shown that in certain operation points it is an advantage to use a multilevel inverter to achieve a higher efficiency for the inverter but is also shown that in some operation points the multilevel inverter increases the losses in the battery. However, it is worth mentioning that there is a controllability on where in the battery the losses should take place.The multilevel inverter can also be used as a two level inverter in these operation points to minimize the battery losses.
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| 4. |
- Josefsson, Oskar, 1985
(författare)
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Investigation of a Multilevel Inverter for Electric Vehicle Applications
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Electrified vehicles on the market today all use the classical two-level inverter as the propulsion inverter. This thesis analyse the potential of using a cascaded H-bridge multilevel inverter as the propulsion inverter. With a multilevel inverter, the battery is divided into several parts and the inverter can now create voltages in smaller voltage levels than the two-level inverter. This, among other benefits, reduces the EMI spectrum in the phase cables to the electric machine. It is also shown that these H-bridges can be placed into the battery casing with a marginal size increase, and some addition of the cooling circuit performance. The benefit is that the separate inverter can be omitted.In this thesis, measurements and parameterisations of the battery cells are performed at the current and frequency levels that are present in a multilevel inverter drive system. The derived model shows a great match to the measurements for different operating points and frequencies.Further, full drive cycle simulations are performed for the two analysed systems. It is shown that the inverter loss is greatly reduced with the multilevel inverter topology, mainly due to the possibility to use MOSFETs instead of IGBTs. However, the battery packs in a multilevel inverter experience a current far from DC when creating the AC-voltages to the electric machine. This leads to an increase of the battery loss but looking at the total inverter-battery losses, the system shows an efficiency improvement over the classical two-level system for all but one drive cycle. In the NEDC drive cycle the losses are reduced by 30 % but in the demanding US06 drive cycle the losses are increased by 11 % due to the high reactive power demand at high speed driving. These figures are valid for a plug-in hybrid with a 50 km electrical range where no filter capacitors are used. In a pure electric vehicle, there is always an energy benefit of using a multilevel converter since a larger battery will have lower losses. By placing capacitors over the inputs of the H-bridges, the battery current is filtered. Two different capacitor chemistries are analysed and experimentally verified and an improvement is shown, even for a small amount of capacitors and especially at cold operating conditions.
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| 5. |
- Kersten, Anton, 1991, et al.
(författare)
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Battery Loss and Stress Mitigation in a Cascaded H-Bridge Multilevel Inverter for Vehicle Traction Applications by Filter Capacitors
- 2019
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Ingår i: IEEE Transactions on Transportation Electrification. - 2332-7782. ; 5:3, s. 659-671
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, two types of filter capacitors of varying capacity, were connected to the battery packs of a cascaded H-Bridge single-star multilevel vehicle traction inverter, and their influence on the battery losses has been analyzed. The battery and capacitor simulation models used are experimentally verified in a down-scaled system. Different capacitor configurations were simulated for four drive cycle scenarios to determine the potentials for the mitigation of current pulse stresses and battery loss reduction with respect to the added weight. By adding capacitors corresponding to a weight of 4% of the initial battery storage, the peak current is reduced by 5%-20%, depending on the operating point from DC to a few kHz, and the battery losses are reduced by 10%. In comparison, it is demonstrated that adding supercapacitors is more beneficial for lower output frequencies, while adding electrolytic capacitors is better for higher output frequencies. Furthermore, the low-order voltage harmonics of the DC-rails between the converter and battery were reduced by 10%-30% for frequencies above 9 kHz, which decreases the potential of electromagnetic disturbances. In addition, during cold battery temperatures, when it is very important to avoid heavy cyclings, the loss reduction using the capacitors was 2.5 times larger than for nominal temperature.
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