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Previous studies have proposed to use cascaded multilevel topologies in stationary battery energy storage systems (BESSs) or in BESSs of electric vehicles, due to the balancing capability or the high efficiency of these topologies. Because of the elimination of the direct current (DC) bus, the batteries in these topologies are expected to experience large current ripples. However, whether these current ripples can accelerate the aging of the batteries has not yet been dedicatedly investigated, although it is a determining factor for the feasibility of this category of topologies. Therefore, this paper first summarizes the existing studies regarding the influence of current ripples on the aging of lithium batteries, which proves the necessity of an experimental investigation. Then a long-term aging experiment on battery cells is conducted, in order to examine the influence of the current ripples in cascaded multilevel topologies. According to the experimental results and the conclusions in previous studies, the ripples in cascaded multilevel topologies generally have a negligible influence on the aging of batteries, except in certain scenarios. These scenarios can be identified by the three preconditions, first, current ripples must contain micro charge and discharge cycles; second, the micro cycles are below 10 Hz; third, low frequency micro cycles must contribute charge large throughput.
Fengqi Chang; Felix Roemer; Markus Lienkamp. Influence of Current Ripples in Cascaded Multilevel Topologies on the Aging of Lithium Batteries. IEEE Transactions on Power Electronics 2020, 35, 11879 -11890.
AMA StyleFengqi Chang, Felix Roemer, Markus Lienkamp. Influence of Current Ripples in Cascaded Multilevel Topologies on the Aging of Lithium Batteries. IEEE Transactions on Power Electronics. 2020; 35 (11):11879-11890.
Chicago/Turabian StyleFengqi Chang; Felix Roemer; Markus Lienkamp. 2020. "Influence of Current Ripples in Cascaded Multilevel Topologies on the Aging of Lithium Batteries." IEEE Transactions on Power Electronics 35, no. 11: 11879-11890.
This paper presents a method to find the optimal configuration for an electric vehicle energy storage system using a cascaded H-bridge (CHB) inverter. CHB multilevel inverters enable a better utilization of the battery pack, because cells/modules with manufacturing tolerances in terms of capacity can be selectively discharged instead of being passively balanced by discharging them over resistors. The balancing algorithms have been investigated in many studies for the CHB topology. However, it has not yet been investigated to which extend a conventional pack can be modularized in a CHB configuration. Therefore, this paper explores different configurations by simulating different switch models, switch configurations, and number of levels for a CHB inverter along with a reference load model to find the optimal design of the system. The configuration is also considered from an economically point of view, as the most efficient solution might not be cost-effective to be installed in a common production vehicle. It is found that four modules per phase give the best compromise between efficiency and costs. Paralleling smaller switches should be preferred over the usage of fewer, larger switches. Moreover, selecting specific existing components results in higher savings compared to theoretical optimal components.
Felix Roemer; Massab Ahmad; Fengqi Chang; Markus Lienkamp. Optimization of a Cascaded H-Bridge Inverter for Electric Vehicle Applications Including Cost Consideration. Energies 2019, 12, 4272 .
AMA StyleFelix Roemer, Massab Ahmad, Fengqi Chang, Markus Lienkamp. Optimization of a Cascaded H-Bridge Inverter for Electric Vehicle Applications Including Cost Consideration. Energies. 2019; 12 (22):4272.
Chicago/Turabian StyleFelix Roemer; Massab Ahmad; Fengqi Chang; Markus Lienkamp. 2019. "Optimization of a Cascaded H-Bridge Inverter for Electric Vehicle Applications Including Cost Consideration." Energies 12, no. 22: 4272.
Although electric buses operate at lower noise levels and without direct emissions, only a small fraction of bus fleets in the world is electrified due to the high investment associated with the battery systems of the electric vehicles and the required charging infrastructure. To make the cost of electrification more competitive, the design of the battery pack and the charging infrastructure should be optimized for the specific operating conditions. In this paper, a method is presented that minimizes the total cost of ownership of the electric bus fleet by choosing the optimal battery size, number of charging stations, and charging power for a given schedule, vehicle characteristics and environmental conditions. The method serves as a decisionmaking aid for automotive engineers in the early vehicle design process and/or for urban transit agencies to select appropriate vehicle models. Implementation of the method in a case study showed that the optimization can reduce the costs that are influenced by the battery and charging infrastructure by 22.8%, compared to the reference vehicle and the charging configuration of the pilot project. This is mainly attributed to the reduced battery pack capacity and the higher utilization ratio of the charging infrastructure.
Olaf Teichert; Fengqi Chang; Aybike Ongel; Markus Lienkamp. Joint Optimization of Vehicle Battery Pack Capacity and Charging Infrastructure for Electrified Public Bus Systems. IEEE Transactions on Transportation Electrification 2019, 5, 672 -682.
AMA StyleOlaf Teichert, Fengqi Chang, Aybike Ongel, Markus Lienkamp. Joint Optimization of Vehicle Battery Pack Capacity and Charging Infrastructure for Electrified Public Bus Systems. IEEE Transactions on Transportation Electrification. 2019; 5 (3):672-682.
Chicago/Turabian StyleOlaf Teichert; Fengqi Chang; Aybike Ongel; Markus Lienkamp. 2019. "Joint Optimization of Vehicle Battery Pack Capacity and Charging Infrastructure for Electrified Public Bus Systems." IEEE Transactions on Transportation Electrification 5, no. 3: 672-682.
There is rapidly growing interest in autonomous electric vehicles due to their potential in improving safety, accessibility, and environmental outcomes. However, their market penetration rate is dependent on costs. Use of autonomous electric vehicles for shared-use mobility may improve their cost competitiveness. So far, most of the research has focused on the cost impact of autonomy on taxis and ridesourcing services. Singapore is planning for island-wide deployment of autonomous vehicles for both scheduled and on-demand services as part of their transit system in the year 2030. TUMCREATE developed an autonomous electric vehicle concept, a microtransit vehicle with 30-passenger capacity, which can complement the existing bus transit system. This study aims to determine the cost of autonomous electric microtransit vehicles and compare them to those of buses. A total cost of ownership (TCO) approach was used to compare the lifecycle costs. It was shown that although the acquisition costs of autonomous electric vehicles are higher than those of their conventional counterparts, they can reduce the TCO per passenger-km up to 75% and 60% compared to their conventional counterparts and buses, respectively.
Aybike Ongel; Erik Loewer; Felix Roemer; Ganesh Sethuraman; Fengqi Chang; Markus Lienkamp. Economic Assessment of Autonomous Electric Microtransit Vehicles. Sustainability 2019, 11, 648 .
AMA StyleAybike Ongel, Erik Loewer, Felix Roemer, Ganesh Sethuraman, Fengqi Chang, Markus Lienkamp. Economic Assessment of Autonomous Electric Microtransit Vehicles. Sustainability. 2019; 11 (3):648.
Chicago/Turabian StyleAybike Ongel; Erik Loewer; Felix Roemer; Ganesh Sethuraman; Fengqi Chang; Markus Lienkamp. 2019. "Economic Assessment of Autonomous Electric Microtransit Vehicles." Sustainability 11, no. 3: 648.
In order to improve the driving range and reduce the cost of battery electric vehicles (BEV) through a higher efficiency, this paper proposes to adopt multilevel converters using low voltage Si MOSFETs in the electric powertrains. A multilevel Si MOSFET inverter, a conventional IGBT inverter and a SiC MOSFET inverter are modelled and compared using a reference vehicle over various driving cycles. The costs of the three solutions are also compared. It is shown that the multilevel Si MOSFET inverter has a rather high efficiency and realizes the lowest cost among the three solutions even when the worst case of cost is considered. Sensitivity analysis also shows that the multilevel Si MOSFET inverter is suitable for a wide range of vehicle concepts in addition to the reference vehicle. Moreover, the multilevel topology also features lower electromagnetic interference (EMI) and provides modularity. Therefore, Si MOSFET-based multilevel inverters are proved in this paper to be an appropriate option to improve the efficiency and reduce the cost of electric powertrains.
Fengqi Chang; Olga Ilina; Markus Lienkamp; Leon Voss. Improving the Overall Efficiency of Automotive Inverters Using a Multilevel Converter Composed of Low Voltage Si mosfets. IEEE Transactions on Power Electronics 2018, 34, 3586 -3602.
AMA StyleFengqi Chang, Olga Ilina, Markus Lienkamp, Leon Voss. Improving the Overall Efficiency of Automotive Inverters Using a Multilevel Converter Composed of Low Voltage Si mosfets. IEEE Transactions on Power Electronics. 2018; 34 (4):3586-3602.
Chicago/Turabian StyleFengqi Chang; Olga Ilina; Markus Lienkamp; Leon Voss. 2018. "Improving the Overall Efficiency of Automotive Inverters Using a Multilevel Converter Composed of Low Voltage Si mosfets." IEEE Transactions on Power Electronics 34, no. 4: 3586-3602.
To better evaluate the configuration of battery packs in electric vehicles (EV) in the early design phase, this paper proposes a mathematic model for the simulation of battery packs based on the elementwise calculations of matrices. This model is compatible with the different battery models and has a fast simulation speed. An experimental platform is built for the verification. Based on the proposed model and the statistic features of battery cells, the influence of the number of paralleled cells in a battery pack is evaluated in Monte-Carlo experiments. The simulation results obtained from Monte-Carlo experiments show that the parallel number is able to influence the total energy loss inside the cells, the energy loss caused by the balancing of the battery management system (BMS) and the degradation of the battery pack.
Fengqi Chang; Felix Roemer; Michael Baumann; Markus Lienkamp. Modelling and Evaluation of Battery Packs with Different Numbers of Paralleled Cells. World Electric Vehicle Journal 2018, 9, 8 .
AMA StyleFengqi Chang, Felix Roemer, Michael Baumann, Markus Lienkamp. Modelling and Evaluation of Battery Packs with Different Numbers of Paralleled Cells. World Electric Vehicle Journal. 2018; 9 (1):8.
Chicago/Turabian StyleFengqi Chang; Felix Roemer; Michael Baumann; Markus Lienkamp. 2018. "Modelling and Evaluation of Battery Packs with Different Numbers of Paralleled Cells." World Electric Vehicle Journal 9, no. 1: 8.
The energy consumption per passenger per kilometre and the total energy consumption of the system are two important criteria in the vehicle concept evaluation for a public transport system. However, the calculation of these two values mainly depends on the trip characteristics of the public transport system, including the trip length and the occupancy of vehicles, which are not readily available to public. The analysis of the massive trip data requires strong computational power and thus long processing time, which is not appropriate for the early phase design of vehicle concept. To calculate the energy consumption of a public transport system, this paper introduces a novel approach only based on variables that are generally open to public, including daily fleet mileage and the daily total ridership. This approach can be rapidly implemented for different vehicles and different public transport systems. Therefore, it can be used for a rapid evaluation of the vehicle concept designs for specific public transport systems. The approach is also useful for power grid planners to quickly decide if the infrastructure is ready for the electrification of the public transport system.
Fengqi Chang; Raymond Khoo; Aybike Ongel; Markus Lienkamp. Rapid Energy Consumption Assessment of Vehicle Concepts for Public Transport Systems without Detailed Deployment Data. 2018 IEEE Innovative Smart Grid Technologies - Asia (ISGT Asia) 2018, 452 -455.
AMA StyleFengqi Chang, Raymond Khoo, Aybike Ongel, Markus Lienkamp. Rapid Energy Consumption Assessment of Vehicle Concepts for Public Transport Systems without Detailed Deployment Data. 2018 IEEE Innovative Smart Grid Technologies - Asia (ISGT Asia). 2018; ():452-455.
Chicago/Turabian StyleFengqi Chang; Raymond Khoo; Aybike Ongel; Markus Lienkamp. 2018. "Rapid Energy Consumption Assessment of Vehicle Concepts for Public Transport Systems without Detailed Deployment Data." 2018 IEEE Innovative Smart Grid Technologies - Asia (ISGT Asia) , no. : 452-455.
Fengqi Chang; Olga Ilina; Omar Hegazi; Leon Voss; Markus Lienkamp. Adopting MOSFET multilevel inverters to improve the partial load efficiency of electric vehicles. 2017 19th European Conference on Power Electronics and Applications (EPE'17 ECCE Europe) 2017, 1 .
AMA StyleFengqi Chang, Olga Ilina, Omar Hegazi, Leon Voss, Markus Lienkamp. Adopting MOSFET multilevel inverters to improve the partial load efficiency of electric vehicles. 2017 19th European Conference on Power Electronics and Applications (EPE'17 ECCE Europe). 2017; ():1.
Chicago/Turabian StyleFengqi Chang; Olga Ilina; Omar Hegazi; Leon Voss; Markus Lienkamp. 2017. "Adopting MOSFET multilevel inverters to improve the partial load efficiency of electric vehicles." 2017 19th European Conference on Power Electronics and Applications (EPE'17 ECCE Europe) , no. : 1.
This paper proposed a modular multilevel topology using power electronics transformers for the modular drivetrain of electric vehicles (EV). Because of its high modularity, the topology can be easily applied to a wide range of EVs, from personal vehicles to passenger cars. Compared with two conventional modular multilevel converters, fewer submodules are needed and its control is thus simpler. The topology can also balance voltage of batteries without an equalization circuit and has low harmonics distortion. Moreover, according to the simulation results, the topology has higher overall efficiency than the conventional 6-switch 2-level inverter structure in synthesized driving cycles.
Fengqi Chang; Markus Lienkamp. A modular multilevel topology using power electronic transformers for the modular drivetrains of electric vehicles. 2016 18th European Conference on Power Electronics and Applications (EPE'16 ECCE Europe) 2016, 1 -9.
AMA StyleFengqi Chang, Markus Lienkamp. A modular multilevel topology using power electronic transformers for the modular drivetrains of electric vehicles. 2016 18th European Conference on Power Electronics and Applications (EPE'16 ECCE Europe). 2016; ():1-9.
Chicago/Turabian StyleFengqi Chang; Markus Lienkamp. 2016. "A modular multilevel topology using power electronic transformers for the modular drivetrains of electric vehicles." 2016 18th European Conference on Power Electronics and Applications (EPE'16 ECCE Europe) , no. : 1-9.