Increasing electric loads in a vehicle causes over-discharge of a battery and drag torque due to an alternator. This paper gives a system concept of vehicle electric power flow management to solve these issues. Its primary function includes preserving electricity in a battery, stabilizing electric bus voltage, interfacing with vehicle torque control system, and improving fuel economy.
The key point to realize such a system is a unified structure. It offers ‘Plug and Play’ function for electric power management components. Newly developed Vehicle Electric Power Flow Management System (VEF ) totally controls electric power flow in a vehicle. VEF contains an Electric Power Manager and its functional sub-systems, and controls them with the key parameter ‘electric power’. The sub-system includes Generation, Storage, Conversion, and Distribution to the loads. While sum of power required by electric loads exceeds a capacity of Generation and discharge of Storage, some electric loads are forced to reduce. These loads are selected according to the sum of required electric power and priority based on the load operating conditions. As VEF has a unified structure, it can be extensively applied for newcomer generators, batteries and loads in various categories of vehicles.
VEF is evaluated with a test vehicle, and the results show that overall experiments are positive, including bus voltage stability and loads limitation with acceptable driver's feeling.