A detailed analysis of a power converter to buffer the battery voltage in lift trucks

To increase the total system efficiency of electric vehicles and the lifetime of traction batteries one approach is connecting electric double layer capacitors in parallel to the batteries via a dc-dc converter. Here, from the efficiency point of view the best voltage range for the capacitors is derived. Based on the maximum capacitor voltage four different dc-dc converter circuits are analyzed, simulated, and compared to each other. The most promising topology is selected, built-up and implemented in an existing lift-truck traction system. Important equations for the design, simulation and selection of the topology are presented. Measurements and simulations prove the benefit of the additional circuit.