Development of High Efficiency Boost DC/DC Converter For EV

Abstract

In this paper, reactorless high efficiency boost DC/DC converter for EV is proposed. In proposed converter, improves efficiency because decrease power loss when the switches are turned on/off using zero current switching (ZCS) at all switch of primary full bridge. By replacing reactance ingredients of L-C resonance circuit for ZCS with leakage inductance ingredients of high frequency transformer, it reduces system size and expense because of not add special reactor. For validity verification of proposed converter, in the paper implements simulation using PSIM and perform experiment by making 5KW DC/DC converter. In experimental results, efficiency of proposed converter conformed superiority. Today the use of electricity is increasing with the development of industries and vehicles with internal combustion engine are rapidly increasing for convenience of travel. To produce electricity and drive internal combustion engines, fossil fuels must be used, causing serious environmental problems. These days many people are making efforts to reduce CO2 which is the main culprit for the destruction of global environment. In particular, as vehicles account for over 50% of the CO2 emissions, active efforts to reduce them are being made all over the world. Typical examples of such efforts are the improvement of fuel economy and the introduction of electric vehicles. Recently, hybrid vehicles that use both internal combustion engine and electric motor have been developed with effective improvement of fuel economy. It is expected that in the future, the percentage of vehicles using internal combustion engine will gradually decrease and ultimately be replaced with pure electric vehicles and fuel-cell vehicles(1)(2). As the use of electric motors is increasing, traction motors mainly use 300 V or higher voltages considering losses and advantages in motor design. However, since such high- voltage power supply systems have such problems as electric shock, systems like NEV (Neighborhood Electric Vehicle) use low voltage batteries of maximum 70 V. Due to safety and efficiency issues, batteries are using low voltage while motors use high voltages. Thus, it is essential to develop a boost DC/DC converter with at least 4-fold boosting efficiency(3)(4). Furthermore, an insulation-type converter needs to be developed to address the electric safety issue. Accordingly, this paper proposes an insulated DC/DC converter that uses a voltage multiplier circuit composed of diodes and condensers at the output for high voltage multiplication, in particular, a new insulation-type DC/DC converter with a serial connection of two voltage multiplier circuits for 4-fold boosting. The proposed method maintained the ratio of the transformer as 1:1 for identical input and output characteristics of the converter considering the regenerative braking of vehicles in the future. Furthermore, the proposed converter reduced the switching loss of the power switch using a serial L-C resonance, and the size and cost of the total system can be reduced by replacing the reactance component required for the L-C resonance circuit with a transformer leakage reactance(5) . To verify the feasibility of the proposed insulated DC/DC converter using a voltage multiplier circuit, a simulation was conducted using PSIM, and the real converter was fabricated and tested. It was found that up to 4-fold boosting was possible with the voltage multiplier circuit and a serial circuit only with no separate control, and the maximum efficiency of the converter was very high at around 97%.