This paper presents a synchronous buck-boost DC-DC converter with coupled inductor which connects the ultracapacitor pack and a DC bus of an electric vehicle. In order to control this kind of DC-DC converter the digital signal processor (DSP) is used. The coupled inductor is used to reduce current ripples in each phase, thus allowing to measure currents in a simple way and improves transient response. The proposed power converter charges ultracapacitor pack to store the kinetic energy during vehicle braking and regenerate this stored energy during next speed up. In the paper the software algorithm of the control loop of the converter is presented. The experimental test of the DC-DC converter was performed using the test platform for DC electric motor of traction vehicle. The presented switched converter can be used for electric vehicle with low-power DC electric motor.