Mid-Term presentation by by Qian Xun.

TIME: 4 June 2020, 10:00-12:00
PLACE: Zoom link: https://chalmers.zoom.us/j/69885771207
SUPERVISOR: Yujing Liu, Electrical engineering, Chalmers University of Technology
OPPONENT: Ola Carlson, Chalmers University of Technology

“​Evaluation of Fuel Cell/Supercapacitor Hybrid Powertrain for Automotive Applications“

ABSTRACT
Fuel cell (FC), with fast-refueling time, high energy density, zero CO2 emission, is becoming a promising solution for future fossil-free transportation. However, a relatively slow dynamic response and inability to recover regenerative energy of FC make an energy buffer, i.e. battery or supercapacitor (SC) is necessary to formulate a hybrid electric vehicle. Due to the unique characteristics of each device, vehicle performance is dependent on different hybridization methods with FC. In this work, three typical hybrid powertrain topologies are compared in terms of energy efficiency. With the absence of any DC/DC converters, the efficiency of FC/SC passive hybrid powertrain is 2% higher in propulsion and 4% higher in regenerative braking than that in semi-active topologies. In the FC/SC passive hybrid system, the power distribution between each device is inherently decided by the internal resistance, and the DC-link voltage also varies with the power demand of the vehicle. Component models including losses and their dependency on machine speed, torque, and DC-link voltage are built and verified. The simulation results show that energy efficiency varies between 53−76% during propulsion for a multiplicity of drive cycles, while it is 85-94% during braking. A 3kW lab-scaled FC/SC passive hybrid system is designed and tested, and it shows that FC takes time to respond to the load change, while SC provides transient power. To achieve full controllability of the power distribution between FC and SC, a boost converter for FC and a buck-boost converter for SC are required. A low-pass filter with adaptive cut-off frequency is used to control the power allocation. The cut-off frequency is regulated based on an artificial potential field approach to avoid to over-charge or over-discharge of SC. A load disturbance compensator is proposed to suppress the DC-link voltage fluctuation during vehicle acceleration and deceleration. The performance of the proposed method is evaluated by simulations and experiments.

Read more here:
https://www.chalmers.se/en/departments/e2/calendar/Pages/Interim-seminar-Qian-Xun.aspx