Modular Battery Systems for Electric Vehicles based on Multilevel Inverter Topologies - Opportunities and Challenges
Doctoral thesis, 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.

Dynamic reconfiguration

Energy storage

Energy efficiency

Drive cycle efficiency

Power MOSFET

vehicles

H-bridge

Multilevel systems

Electromagnetic compatibility

Modular battery systems

Battery system performance

Modular multilevel converters

Conduction losses

Electric vehicles

Batteries

Dual battery pack

Cascaded converters

DC-AC power converters

BMS

Common mode noise

Battery modeling

vehicle electrification

Lecture room HB1
Opponent: Professor Remus Teodorescu, Aalborg University

Author

Anton Kersten

Chalmers, Electrical Engineering, Electric Power Engineering

Efficiency of Active Three-Level and Five-Level NPC Inverters Compared to a Two-Level Inverter in a Vehicle

2018 20th European Conference on Power Electronics and Applications, EPE 2018 ECCE Europe,; (2018)p. 1-9

Paper in proceeding

Fault Detection and Localization for Limp Home Functionality of Three-Level NPC Inverters with Connected Neutral Point for Electric Vehicles

IEEE Transactions on Transportation Electrification,; Vol. 5(2019)p. 416-432

Journal article

CM & Line-Dm Noise Separation for Three-Level NPC Inverter with Connected Neutral Point for Vehicle Traction Applications

ITEC 2019 - 2019 IEEE Transportation Electrification Conference and Expo,; Vol. June 2019(2019)p. 1-6

Paper in proceeding

LiFePO4 Battery Modeling and Drive Cycle Loss Evaluation in Cascaded H-Bridge Inverters for Vehicles

ITEC 2019 - 2019 IEEE Transportation Electrification Conference and Expo,; Vol. June 2019(2019)p. 1-7

Paper in proceeding

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

IEEE Transactions on Transportation Electrification,; Vol. 5(2019)p. 659-671

Journal article

Exponential Modular Multilevel Converter for Low Voltage Applications

2019 21st European Conference on Power Electronics and Applications, EPE 2019 ECCE Europe,; (2019)p. 1-11

Paper in proceeding

Inverter and Battery Drive Cycle Efficiency Comparisons of CHB and MMSP Traction Inverters for Electric Vehicles

2019 21st European Conference on Power Electronics and Applications, EPE 2019 ECCE Europe,; (2019)p. 1-12

Paper in proceeding

Analysis and estimation of the maximum circulating current during the parallel operation of reconfigurable battery systems

2020 IEEE Transportation Electrification Conference and Expo, ITEC 2020,; (2020)p. 229-234

Paper in proceeding

Elimination/Mitigation of Output Voltage Harmonics for Multilevel Converters Operated at Fundamental Switching Frequency using Matlab's Genetic Algorithm Optimization

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

Paper in proceeding

Online and On-Board Battery Impedance Estimation of Battery Cells, Modules or Packs in a Reconfigurable Battery System or Multilevel Inverter

IECON Proceedings (Industrial Electronics Conference),; (2020)p. 1884-1891

Paper in proceeding

Next-Generation Battery Management Systems: Dynamic Reconfiguration

IEEE Industrial Electronics Magazine,; Vol. 14(2020)p. 20-31

Journal article

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

IEEE Transactions on Industrial Electronics,; Vol. 68(2021)p. 6682-6691

Journal article

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

IEEE Transactions on Industrial Electronics,; Vol. 69(2022)p. 5931-5941

Journal article

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.

Loss and EMI reduction in electrified vehicle through the usage of a multilevel converter

Swedish Energy Agency (44807-1), 2017-07-01 -- 2021-12-31.

Areas of Advance

Transport

Energy

Subject Categories

Vehicle Engineering

Electrical Engineering, Electronic Engineering, Information Engineering

Energy Systems

Control Engineering

Signal Processing

Other Electrical Engineering, Electronic Engineering, Information Engineering

ISBN

978-91-7905-587-5

Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 5054

Publisher

Chalmers

Lecture room HB1

Opponent: Professor Remus Teodorescu, Aalborg University

More information

Latest update

3/22/2022