SAE 2014 Vehicle Electronics and Powertrain Technologies Forum
Technical Session Schedule
Thursday, December 11
Fuel Cell Control Systems
(Session Code: VEP4)
Room Grand Ballroom A&B 2:00 p.m.
Fuel cell vehicles are now being commercialized in various markets throughout the world. This session will look at various control strategies to maximize the benefits of this emerging technology.
|| ORAL ONLY
|Lifetime Analysis of Fuel Cell in a Bus Hybrid Powertrain
Studies have shown that operating conditions, especially high cell voltage occurring during idle
running of the vehicle, and load cycling, are major contributors to chemical and mechanical degradation
of the fuel cell [1, 2]. With aim to link these findings with the hybrid powertrain design and operation, we
have demonstrated the effect of power management in the hybrid system on the fuel cell lifetime by
comparing two scenarios: First, we analyzed the operational data from hybrid fuel cell busses in Whistler,
BC, Canada. Second, an alternate power management scheme was considered for the same size stack,
where the dynamics of the load were primarily handled by the battery instead of the fuel cell.
The Whistler fuel cell bus fleet is powered by Ballard FCvelocityTM-HD6 150kW modules in a hybrid
configuration with a 47kW Li-Ion battery pack. A sample data from five buses, for 300 hours of operation
was selected evenly from summer and winter. The average power of the fuel cell was 72kW and its load
cycle showed tracking the peak demands of the load almost completely. The contribution from the battery
was small, with maximum of 5% state-of-charge (SoC) utilization for the entire operation. To quantify the
voltage state of the stack, the average cell voltage was quantized into "low", "medium", and "high" bins.
The duration at which the voltage was in each bin was then obtained and fed to a degradation estimation
model, developed in-house, to find the lifetime of the stack.
Alternatively, we hypothesized a modified power management scheme for the same hybrid setup, where
the dynamics of the load were "filtered" by the battery. The fuel cell, in this “load leveling” scenario,
functions as a battery charger (similar to a series hybrid car) relying on wider range of battery SOC
utilization, delivering constant (average) power to the hybrid system. The degradation of the fuel cell was
estimated using the same technique as above.
We have observed that when the fuel cell operates in a constant-power mode, the expected lifetime is
more than doubled. The results imply that with proper sizing of the storage components in the hybrid
system (battery and/or ultracapacitor), and optimizing the power management controller to shift the
dynamics of the load to the storage(s), we can considerably extend the lifetime of the fuel cell which
decreases the total cost of ownership of the overall powertrain.
Buz A. McCain, Ballard Power Systems Inc.