PhD Thesis - Cranfield University

Chapter 5
In this strategy, only P battmax is varied throughout the decision epochs with all other outputs
held at constant values determined by design. The influence of the EMS over a standard
US06 schedule is illustrated in Figure 5.16 and Figure 5.17. With both simulations, the
starting SoC of the ultracapacitors are equal and set just below the maximum value. In
Figure 5.16, the EMS is not activated and so the power split between the battery and
ultracapacitor is determined by the fixed policy constraints of the PMS. Ultracapacitor
power is only required when the load demand exceeds the defined battery capability and no
intervention of its target SoC is performed. As shown in the second graph of Figure 5.16,
during the second deceleration to zero speed event the ultracapacitor is charged via
regenerative braking but only to its maximum SoC. For illustration purpose, the SoC graph
of Figure 5.16 shows the rise of SoC above the maximum value as the extra capacity
required to harness the regenerative energy. In this scenario, the activation of dissipative
(dynamic) brakes is required. This is shown in the bottom graph of Figure 5.16.
Disipative Brake Activation
(Boolean)
(km/h)
(pu)
1
Figure 5.16 Simulation of ultracapacitor SoC without the EMS.
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SoC
Max
(Activation of dissipative brakes is necessary to absorb access regenerative power)