Modular Battery Systems for Electric Vehicles based on Multilevel Inverter Topologies - Opportunities and Challenges
Doktorsavhandling, 2021

Modular battery systems based on multilevel inverter (MLI) topologies can possibly overcome some shortcomings of two-level inverters when used for vehicle propulsion. The results presented in this thesis aim to point out the advantages and disadvantages, as well as the technical challenges, of modular vehicle battery systems based on MLIs in comparison to a conventional, two-level IGBT inverter drivetrain. The considered key aspects for this comparative investigation are the drive cycle efficiency, the inverter cost, the fault tolerance capability of the drivetrain and the conducted electromagnetic emissions. Extensive experiments have been performed to support the results and conclusions.

In this work, it is shown that the simulated drive cycle efficiency of different low-voltage-MOSFET-based, cascaded seven-level inverter types is improved in comparison to a similarly rated, two-level IGBT inverter drivetrain. For example, the simulated WLTP drive cycle efficiency of a cascaded double-H-bridge (CDHB) inverter drivetrain in comparison to a two-level IGBT inverter, when used in a small passenger car, is increased from 94.24% to 95.04%, considering the inverter and the ohmic battery losses. In contrast, the obtained efficiency of a similar rated seven-level cascaded H-bridge (CHB) drivetrain is almost equal to that of the two-level inverter drivetrain, but with the help of a hybrid modulation technique, utilizing fundamental selective harmonic elimination at lower speeds, it could be improved to 94.85%. In addition, the CDHB and CHB inverters’ cost, in comparison to the two-level inverter, is reduced from 342€ to 202€ and 121€, respectively.

Furthermore, based on a simple three-level inverter with a dual battery pack, it is shown that MLIs inherently allow for a fault tolerant operation. It is explained how the drivetrain of a neutral point clamped (NPC) inverter can be operated under a fault condition, so that the vehicle can drive with a limited maximum power to the next service station, referred to as limp home mode. Especially, the detection and localization of open circuit faults has been investigated and verified through simulations and experiments.

Moreover, it is explained how to measure the conducted emissions of an NPC inverter with a dual battery pack according to the governing standard, CISPR 25, because the additional neutral point connection forms a peculiar three-wire DC source. To separate the measured noise spectra into CM, line-DM and phase-DMquantities, two hardware separators based on HF transformers are developed and utilized. It is shown that the CM noise is dominant. Furthermore, the CM noise is reduced by 3dB to 6dB when operating the inverter with three-level instead of two-level modulation.

Power MOSFET

H-bridge

Modular battery systems

DC-AC power converters

vehicle electrification

Electric vehicles

Battery modeling

Common mode noise

Multilevel systems

Batteries

Electromagnetic compatibility

vehicles

BMS

Energy efficiency

Dual battery pack

Battery system performance

Dynamic reconfiguration

Energy storage

Drive cycle efficiency

Cascaded converters

Modular multilevel converters

Conduction losses

Lecture room HB1
Opponent: Professor Remus Teodorescu, Aalborg University

Författare

Anton Kersten

Chalmers, Elektroteknik, Elkraftteknik, Elmaskiner och kraftelektronik

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Battery Loss and Stress Mitigation in a Cascaded H-Bridge Multilevel Inverter for Vehicle Traction Applications by Filter Capacitors

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2020 22nd European Conference on Power Electronics and Applications, EPE 2020 ECCE Europe,; (2020)p. 1-12

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Analytical Conduction Loss Calculation of a MOSFET Three-Phase Inverter Accounting for the Reverse Conduction and the Blanking Time

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Analysis and Estimation of the Maximum Switch Current during Battery System Reconfiguration

IEEE Transactions on Industrial Electronics,; Vol. In press(2021)

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To constrain global warming, the transportation sector's CO2 emissions need to be reduced. Therefore, combustion engine vehicles will be increasingly replaced by electric vehicles. For the electrification of passenger vehicles, lithium-ion batteries seem to be the preferred choice as energy storage.

Typically, a two-level propulsion inverter with a single battery pack is used in modern battery electric vehicles. However, the two-level inverter topology does not provide any fault tolerance capability, it bears a high risk for unwanted electromagnetic inferences and individual battery cells can degrade at different rates and significantly reduce the battery pack performance. In contrast, modular battery systems based on multilevel inverter topologies can possibly overcome some shortcomings of two-level inverters when used for vehicle propulsion.

This thesis explores the advantages and disadvantages, as well as the technical challenges, of modular battery systems based on different multilevel inverter topologies in comparison to a classical, two-level IGBT inverter drivetrain for vehicle propulsion applications. The key aspects considered for this
comparative investigation are the drive cycle efficiency of both the inverter and the battery system, the electromagnetic emission levels, the system’s fault tolerance capability and the inverter cost. In addition, advanced online or on-board capable battery diagnostics are derived.

Förlust- och EMI-reduktion i elektrifierat fordon via användande av multinivåomriktare

Energimyndigheten (44807-1), 2017-07-01 -- 2021-12-31.

Styrkeområden

Transport

Energi

Ämneskategorier

Farkostteknik

Elektroteknik och elektronik

Energisystem

Reglerteknik

Signalbehandling

Annan elektroteknik och elektronik

ISBN

978-91-7905-587-5

Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 5054

Utgivare

Chalmers tekniska högskola

Lecture room HB1

Opponent: Professor Remus Teodorescu, Aalborg University

Mer information

Senast uppdaterat

2021-11-07