\ Medium vehicle speed region: When the vehicle speed is greater than V_{vehicle_low} and less than V_{vehicle_high}, the ICE provides the required torque and the speed of the ICE is proportional to the speed of the vehicle.

High vehicle speed region: When the vehicle speed is higher than V_{vehicle_high}, the ICE operates at its maximum speed n_{ice_max}. The following cases are possible in this mode of operation:

1. In case the ICE, operating at n_{ice_max}, cannot meet the required torque and the batteries have SOC lower than SOC_min, then the ICE is forced to operate at speed greater than n_{ice_max} to meet the required torque demand and the EM is de-energised.
2. In case the SOC is greater than SOC_min, the ICE speed is controlled at its specified speed n_{ice_max} , and the remainder torque is produced by the TM.
3. In case the required torque is smaller than the what the ICE can give operating at optimal throttle position (point K in Figure 9 ), and the SOC of the battery is less than SOC_min, the ICE is operated at point K and the TM works as a generator to charge the batteries. The EM is de-energised in this mode of operation.
4. If the SOC of the battery is between SOC_min and SOC_max and the required torque is less than what ICE can deliver at optimal throttle position, the ICE alone provides the required torque. The TM and EM are de-energised in this mode of operation.

 

 

References:

[1] M. Ehsani, Modern Electric, Hybrid Electric and Fuel Cell Vehicles: Fundamentals, Theory and Design , CRC Press, 2005