Design Of Battery Charger For Electric Vehicle Based On SOC Estimation Algorithm

With the increasing depletion of oil resources, and worsening environmental pollution, Fuel-engined vehicle will be gradually replaced by new energy vehicles. It is the inevitable trend. The moment, at home and abroad, a great deal of manpower and material resources have being invested in the development of new energy vehicles, particularly the study of electric vehicles development technologies has been achieved. However, the electric vehicles are still at the experimental stage. It will take some time for a wide range of use. There are so many reasons, such as short electric mileage, frequent and long charging time, short life and high-value of power batteries.It is the ideal way for battery quick charge to control the battery to charge according to the battery characteristics curve. Currently, the charging method based on terminal voltage of batteries is commonly used, which has the advantage of simple control and easy to implement, but it is not ideal from the point that following the battery charging curve. Furthermore, some batteries were easy to be overcharged, so charge times f battery to be reduced.To solve the above problem, lithium iron phosphate cell was taken as the charge object. Based on battery SOC (State Of Charge)-estimated value, the charging strategy of four sections-charging is proposed, and the performance of charger is improved by following the charging curve, meanwhile, power feedback method was used to achieve balanced-charge between each battery, over-charge phenomenon of single battery was avoided, and quick-charge and balanced-charge was achieved. So the battery's charging times could be increased.Developing situation of electric vehicle and its key technology was introduced, the basic principle of charging technologies in electric vehicle is described. The main charging circuit was designed to be phase-shifted full bridge ZVS (zero voltage switching) converter circuit. The phase-shift PWM control mode is studied, and the results were analyzed with the Matlab simulation, and a balanced-charge circuit was proposed. Considering TMS320LF2407 as the core chip, the system control circuit was designed. Analysis of the nonlinear characteristics of SOC and the relevant factors affecting battery SOC estimation, from the precision and the estimate of real-time view, the existing SOC estimation methods were compared, using Ah counting method with Kalman filtering method to achieve SOC estimates, and the SOC estimation algorithm was designed. Based on the SOC estimated value, the control strategy that four paragraphs of charge curve and balanced-charge is studied. PID algorithm was implied to regulate output current and output voltage of the charger, while the system software is designed. Finally, a test machine platform is set up and the result of design was verified.