Modularized High Power Density Bidirectional Buck-Boost DC-DC Converter for EV Battery Management

In electrical vehicles (EV), regenerative braking generates more power than the batteries can accept, which means additional power is wasted to heat in the vehicle's brake pads. And the battery life span will be greatly reduced at a peak power many times that of most battery technologies. Therefore, a compact power unit is needed in parallel with the dc bus to absorb and store the motor generated energy into ultracapacitors. Then ultracapacitors release that power when the vehicle accelerates and the batteries are under the greatest strain. In this paper, a modularized high power density bidirectional dc-dc converter is developed to perform the energy transfer between battery string and ultracapacitors. And a so-called dual current loop control strategy is applied to enhance the converter modularization capability. Experimental results are provided to demonstrate effectiveness of the proposed control strategy. The hardware prototype is capable of achieving 4 kW 42 inch(3) power density and 95.5% efficiency.