International Conference on Renewable Energies and Power Quality (ICREPQ’13) Bilbao (Spain), 20 th to 22 th March, 2013 Renewable Energy and Power Quality Journal (RE&PQJ) ISSN 2172-038 X, No.11, March 2013 Modular Design of DC-DC Converters for EV battery fast-charging Rómulo Antão, Tiago Gonçalves, Rui Escadas Martins Department of Electronics, Telecommunications and Informatics Universidade de Aveiro Campus of Santiago , 3810-193 Aveiro (Portugal) Phone:+351 234 370 355, e-mail: romuloantao@ua.pt Abstract. Electric vehicles (EV) are emerging as a viable and environment-friendly solution for the daily commute. However, for a broader utilization of the EV, their autonomy range has to be increased. A well dispersed charging network and a fast and efficient battery charger system becomes one important factor for the success of the EV. This paper addresses the challenges of developing such High Power chargers and proposes a modular, easily scalable and efficient implementation of a switch-mode DC-DC converter for performing the constant-current/ constant- voltage battery charging process. Key words Electric vehicles charging system, switch-mode DC-DC converters, Forward Topology 1. Introduction The high volatility of the crude oil price and the climate changes are one of the major concerns of nowadays global society. The high dependency of the economy in oil resources and near future reserves depletion brought great investment on alternative and cleaner energy sources. In recent years, the automotive industry grew particular interest on the development of electric vehicles (EV), mainly due to the higher efficiency of electric motors, cheaper electricity prices and the reduction of green-house gas emissions that cars directly produce. Nowadays, plug-in hybrid electric vehicles (PHEV) are the approach adopted by many automobile manufacturers. The existing PHEV's were designed aiming an all-electric range compatible to the daily commuter requirements. They have small capacity batteries, typically 5kWh and can be completely charged typically in a 1h30m period using the regular electrical outlet of 230V/16A. This charge time is perfectly compatible with an employee daily work schedule. The challenge poses, however, on the current generation of EV, which rely their autonomy totally on the battery capacity. For an increased market penetration, the range anxiety of the drivers is the chief concern to overcome. The new Nissan Leaf, one of the 2011 EV models, took a leap ahead, by integrating a 24 kWh battery offering a reported 160 Km autonomy, a concept which has been more recently followed by Opel/Chevrolet, Mitsubishi, Renault and others. However, the state-of-the-art of battery technology still poses big constrains in their power density, charging current, number of charging cycles and ultimately their cost. The lithium-ion batteries currently used combined with a high power charger (under constant current control) allow to achieve 80% of the maximum battery capacity of a vehicle like Nissan Leaf in less than 30 minutes (what still limits the usage of EV for longer distance trips). Until further advances are obtained in the battery research area, charging infrastructures have to be broadly available. According to the developments recently unveiled by the SAE International J1772 committee [1], the battery charging systems can be classified in terms of their power level, and consequently their charging time. Considering the systems with higher power ratings, commonly known as DC fast charging systems, their specifications are following presented:  DC Level I - The car battery is charged directly by a off-board DC charging infrastructure, being supplied a DC voltage (between 200V and 500V) with a current up to 80A, with a maximum power level up to 40KW.  DC Level II - The car battery is charged directly by a off-board DC charging infrastructure, being supplied a DC voltage (between 200V and 500V) allowing a maximum of 200A with a maximum power level of 100kW. There exists however some controversy on the DC charging process control standards existing already a widely used standard, CHAdeMO [2], that specifies the DC fast charger systems up to a maximum power of 62.5kW. Despite the divergences considering protocols and connection standards, the development of such high power systems brought to discussion a common concern regarding the capability of the existing electric grids in supporting such power demanding systems and how the grid quality parameters, such as harmonic distortion and the power factor, will be affected. This analysis is particular important considering the higher power charging systems. By being on the lower layers of the electric mobility supply chain, the way they are developed https://doi.org/10.24084/repqj11.360 528 RE&PQJ, Vol.1, No.11, March 2013