TABLE OF CONTENTS The choice of energy storage system technology is interleaved with vehicle tractive effort for the customer usage pattern anticipated. An example will help clarify the process. In this example a 27 seat city bus is converted to a series hybrid by adding a generator to its CNG fuelled ICE. The bus is assumed to have standing room for an additional 25 passengers. The bus has a total length of 12.5 m, height of 2.85 m and width of 2.5 m and weights 17 500 kg with no passengers and a half tank of fuel. Loaded, and for a 34 : 66% split front to rear, the resultant axle loads are 7300 kg and 14 200 kg. Maximum speed is 90 kph and it is desired to accelerate at 0.11 g and brake at 0.051 g nominal. The CNG fuelled ICE is rated 208 kW with a 75 kW generator. Battery and capacitor pack energy storage is required to supply 113 kW. Electric energy storage is based on nickel-cadmium technology in parallel to an ultra-capacitor bank. The traction system bus voltage is set at U bus-max = 500 V dc maximum and allowed to droop to U bus-min = 400 V dc minimum. For Ni-Cd, U cell = 1.35 V nominal, U cell-max = 1.4 V and U cell-dchg = 1.1 V.
The usage pattern, or drive cycle, for the city bus circuit will be modelled...
