Design and Control Principles of Plug-In Hybrid Electric Vehicles

As discussed in the previous chapters, in the PPS charge sustained hybrid drive train, the net energy consumption in PPS in a complete driving cycle is zero, that is, the energy level in the PPS at the beginning of the driving cycle is equal to the energy level at the end of the driving cycle. All the propulsion energy comes from the primary energy source: gasoline or diesel for IC engines; hydrogen or hydrogen-based fuel for fuel cells. During operation, the energy in the PPS fluctuates in a narrow window. The PPS size is determined by power rather than energy capacity. The energy-to-power ratio is in the range of 0.05–0.1 kWh/kW. That is to say, with a given power capacity, the energy storage in PPS is considered to be sufficient if it can sustain 0.05–0.1 h with the given power. Thus, the PPS is more an energy buffer than energy storage. This is also the origin of the name PPS (peaking power source). At present and in the immediate future, ultracapacitors and high-power batteries or their combination are the most promising candidates as the PPS of the PPS charge sustained HEVs (for details, refer to Chapter 12 of Peaking Power Source and Energy Storage).