Researchers at the University of Waterloo (Canada), with a colleague in Sweden, have used a power management strategy greatly to extend the durability of onboard fuel cells in a plug-in hybrid electric vehicle: an increase of 1.8, 4.8 and 6.9 times, respectively, for an urban, highway and a combined urban-highway driving cycle. A paper on their work is published in the journal Applied Energy.
Fuel cell plug-in hybrid electric vehicles (FC-PHEVs) can have extended range while utilizing cheap grid electricity, but has poor durability of onboard fuel cells due to dynamic loading. In this study, fuel cell durability is enhanced significantly for a novel configuration of FC-PHEVs with three fuel cell stacks through strategic power management by making each fuel cell stack work only at a fixed operating point (i.e., constant output power) and by shortening its active time (operation) via on-off switching control. A hysteresis control strategy of power management is designed to make the active time evenly distributed over the three fuel cell stacks and to reduce the number of on-off switching.
… This enhanced fuel cell durability is derived from the fact that the average power demand of real-time driving cycles is only a fraction of the maximum power that FC-PHEVs could provide, and substantially increased durability can be used to reduce the over-design, hence the cost, of fuel cells.—Zhang et al.
Over the lifetime of a vehicle, the actual power demand of real-time driving cycle is only a fraction—typically 1/4 to 1/3—of the maximum power a vehicle powertrain system can provide, the researchers reasoned. To exploit this, they devised a three-fuel-cell-stack architecture consisting of two types of power suppliers: three fuel cell stacks and one battery.
Architecture of FC-PHEVs with three fuel cell stacks as considered in the Zhang et al. study. The arrows in the diagram indicate the electrical connection for the power flow.
PEM fuel cells have optimal durability when operating at a fixed load (or output power), with significantly reduced durability for a variable load operation. Thus, each fuel cell stack in the configuration operates only at a fixed operating load condition (hence, fixed output power) when it is activated (or on); otherwise, it is shut down (or off).
The three fuel cell stacks have equal design power rating. The main advantage of this design is to achieve the best durability possible for fuel cells by fixing their operating load and reducing their active time.
With our design approach, the cost could be comparable or even cheaper than gasoline engines. The future is very bright. This is clean energy that could boom.—Xianguo Li, director of the Fuel Cell and Green Energy Lab at Waterloo
Hongtao Zhang, Xianguo Li, Xinzhi Liu, Jinyue Yan (2019) “Enhancing fuel cell durability for fuel cell plug-in hybrid electric vehicles through strategic power management,” Applied Energy, Volume 241, Pages 483-490 doi: 10.1016/j.apenergy.2019.02.040