Parallel-series hybrid vehicles battery requirements

The cost dependency on a minimized cell size for Ni-MH and VRLA batteries is shown in Fig. 11.21. In these cases, VRLA is limited by life and Ni-MH is limited by power. At the energy levels required for parallel-series hybrid vehicles, it can be shown that the watt-hour life cost of Ni-MH would have to exceed 33 times that of VRLA, which is not the case even today with prototype batteries. The initial cost consideration that tipped the favour to VRLA for soft hybrids is far less impressive with parallel or series hybrids, since it can be further demonstrated that, even on an initial cost basis, VRLA is about 60% of the cost of the equivalent Ni-MH battery for the parallel-series application, well outside of the bounds where trade-off to initial cost could be considered. 

High-voltage safety considerations require that the architecture of parallel- and series-hybrid vehicles include an integral BMM such that the battery can be controlled from within the pack. This assumes that the battery will be of an advanced design, such as Ni-MH, where safety requires fast, reliable, and self-contained communication with the contactor and charger. 

A car company wants to design a battery for their hybrid vehicle. The battery requirement for this system is 300 V with a nominal capacity of 3.0 kW hr. Suppose they have a 5 A hr cell at 2.0 V. (a) How many cells will be required to make the required battery (b) How many cells will be in series and how many in parallel (Bhardwaj)... 

As shown in Fig. 9.4, in parallel hybrid power circuits the fuel cell delivers power to the motor and charges the battery when required. It also provides extra power to the motor for acceleration once the battery is fully charged. In the case of a series hybrid power circuit, all the power is delivered by battery so it needs to be large. The function of the fuel cell is only to charge the battery depending on driving conditions it can be of relatively low power. Such vehicles generally use alkaline fuel cells. 

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