Hybrid Energy Storage System interface for Electric Vehicles

Abstract

In conventional EV powertrain, Battery is the sole energy storage. This makes higher transient current stress on battery during operation, which shall reduce the life of the battery considerably. The size of the battery may required to be over rated to take care heavy transient demands with respect to its C rating. The regenerative braking capability of Electric power train is also gets limited due to the charging transient limitations in Battery. This eventually results in poor EV power train designs and vehicle performance. A hybrid energy storage system with Battery as primary energy source and Ultra capacitor as transient power manager is proposed as a viable solution. The combination shall provide better utilization of regenerative power, thus increase overall efficiency and range. The secondary storage can absorb all transients during regeneration and supply transients when required, during motoring. This can reduce the transient stress on battery increase the life. Cost effective Power train solution is also a major challenge in practical EV system design, and the proposed architecture is without dedicated DCDC converter for battery. The control logic can be formulated so as to meet the transient supplies of the load by ultra-capacitor and indirectly reduce that from battery. This provides low capacity DC-DC converter design, which could be appropriately overloaded for transient demands, thus reducing the overall size also. This can reduce the overall cost of EV power train. This paper discusses Hybrid Energy Storage System configuration for Battery Electric Vehicles and its Power Management strategy. The ultracapacitor is connected to DC bus using bidirectional converter in current control mode. Power split mechanism is implemented such that, drive current transient requirements, is met by the ultracapacitor depending on its voltage condition and remaining current requirement is met by battery.