PhD Thesis - Cranfield University

Chapter 5
(W)
(km/h)
(pu)
1
Figure 5.17 Simulation of ultracapacitor SoC wit the EMS active.
(The EMS drives the ultracapacitor SoC down during high velocity)
The activation of the EMS with the fuzzy inference engine to regulate the ultracapacitor SoC
in relation to the vehicle speed is shown in Figure 5.17. As shown in the second graph of
Figure 5.17, the EMS drives the ultracapacitor SoC down as the vehicle cruises at high
velocity. The EMS senses that both the vehicle and the ultracapacitor SoC falls in a HIGH
membership function and thus reduces the maximum battery power reference value
(P battmax) fed to the PMS. Since the policy of the PMS mandates the power balance equation
(5-28) be satisfied, the ultracapacitor power is increased to compensate for the battery power
limit. This effectively reduces the ultracapacitor SoC in anticipation of a regenerative event.
Comparing the ultracapacitor power graphs of Figure 5.16 and Figure 5.17, shows that with
the EMS activated, more ultracapacitor power is used at high velocity to regulate the target
SoC. The use of dissipative brakes is not required in the second scenario as the
ultracapacitors are receptive to regenerative energy.
The results satisfactory demonstrate the concept of the hierarchical execution of an energy
management strategy. It exemplifies the downstream propagation of EMS strategy directives
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SoC
Max