On-Line SOC Estimation for Battery of Wireless Tramcar

Abstract

Battery driven tramcars (wireless tramcars) have reached the actual application stage. The most important factor to be considered during the operation of the tramcar is the state of charge (SOC) of the battery. The purpose of this study is to develop on-line method for SOC estimation; the method employs an equivalent circuit of a battery. SOC estimation using a conventional equivalent circuit results in a large error during fast current transients. In order to improve the accuracy of the estimation, we propose the use of a equivalent circuit of a Li-ion battery. Experimental results show that the accuracy of SOC estimation is better when the proposed circuit is used as compared to the accuracy when a conventional equivalent circuit is employed. However, the proposed equivalent circuit results in an error when the temperature of the battery varies. Therefore, we propose a new method for SOC estimation in which the temperature is taken into consideration. This method requires only the measurement of the voltage and current, and therefore, temperature measurement is not required. Experimental results show that the accuracy of the proposed method is greatly improved with the temperature is taken into consideration. The proposed method can be applied to actual wireless tramcar.