Acronyms

within a small range. Thus, the fuel consumption can be reduced. The calculated energy efficiencies of the ESS are shown in Figure 9h. The average energy efficiency is very close to the results of the rule-based strategies. The output voltage and current are given in Figures 9i and j, respectively. The output voltage is proportional to the SOC. The optimal current demonstrates a similar tendency as that of the power follower control. However, more spikes occur at the driving

Science,Technology and Advanced Application of Supercapacitors

The optimal equivalent fuel consumption is 15.72 L/100 km listed in Table 2. Compared to the conventional transit bus, the optimal fuel consumption of the hybrid bus can be decreased by 57% if the quantity of fuel consumed during the starting processes is ignored. In practice, the fuel consumption including starting process will be increased slightly. Taking the optimal result as a reference, the fuel consumptions of the rule-based control strategies are increased by approximate

In this chapter, the energy efficiency of a series hybrid transit bus powered by a

1. The performance of the designed series hybrid transit bus powered by a CNG engine and supercapacitors can fulfill the requirements of the vehicle. Because supercapacitors take advantage of low energy loss and can recover the vehicle's kinetic energy efficiently during regenerative braking, the fuel

significantly by approximately 52% compared to a conventional transit bus under the CTBCDC driving cycle. The results indicate that supercapacitors

power follower control strategy is slightly greater than that of the thermostatic control strategy because the operation current of the ESS remains at a low level. The thermostatic control has a relatively simple logic and less starting times compared with the power follower control. In practice, the most suitable control strategy should be selected according to the requirements of system performance including efficiency, cost, size, reliability, emissions, and

3. The maximum energy efficiency of the designed series hybrid powertrain is estimated using an optimal algorithm based on dynamic programming. The optimal fuel consumption can be decreased by 57% compared to the results of the conventional transit bus. Although the fuel consumption from the rulebased control strategies is slightly higher than that of the optimal control, taking into account the operation requirements of the engine, the rule-based control strategies are more practical for real-time application. However, the result of the optimal control provides some useful insights for real-time control

CNG engine and supercapacitors was evaluated. A mathematical model was established, and three different control strategies were designed. The performance characteristics of two rule-based control strategies were compared to the result of the optimal control using dynamic programming. Based on our analysis, the fol-

consumption of the designed series hybrid powertrain is decreased

2. The energy efficiency of the designed series hybrid transit bus using the

are a good solution for the ESS of the hybrid transit bus.

conditions.

1.7 L/100 km.

6. Conclusions

so on.

strategy design.

132

lowing can be concluded:

