Electric Vehicle Battery Life Extension Using Ultracapacitors and an FPGA Controlled Interleaved Buck-Boost Converter

This paper describes the implementation of a hybrid energy storage system (HESS) using ultracapacitors (UCs) to protect the batteries of an electrical vehicle (EV) from high-peak currents and therefore extend their lifetime. A field-programmable gate array (FPGA) controlled interleaved bidirectional buck-boost converter working in a discontinuous conduction mode, has been designed to transfer the energy between the batteries and the UCs. The FPGA is responsible of generating all the converter gate signals and implements the control stage needed to smooth the battery current peaks. The control strategy is based on dividing the current demand of the motor into two parts (high-frequency current and low-frequency current), the batteries supply the low frequency part and the UCs supply the high-frequency part. Experimental tests have been carried out driving the EV under different scenarios. Experimental results demonstrate the good behavior of the proposed HESS, although the potential battery life extension is still under quantification. The consumption of the EV has been increased due to the converter losses, this increase is minimum under typical driving scenarios, but is quite important in start-stop driving cycles.