Equivalent state of charge estimation method of hybrid energy storage system for electric vehicles based on multiple operating modes

The hybrid energy storage system (HESS) for electric vehicles (EVs) is a network system composed of DC/DC converters, lithium-ion batteries, supercapacitors and etc., which has a complicated coupling relationship. The real-time residual available energy of this system highly depends on the operating modes of the system and cannot be simply evaluated with traditional state of charge SOC estimation techniques. To tackle this challenge, an equivalent ESOC index is proposed to describe the residual available energy of HESS under different operating modes. In addition, a novel estimation method based on the comprehensive weight factor is designed to obtain ESOC in this paper. Firstly, the operation state of the HESS is classified as five different modes according to the demand power of the EVs. Next, considering the working characteristics of the HESS, the weight factors of each operating mode are obtained by using its simulation operation data under three typical vehicle driving cycles. Then, the application effect of the proposed ESOC estimation method is evaluated. Finally, the results indicate that the ESOC index can reflect the residual available energy and power output capacity of the HESS under different operating modes, which is helpful for drivers to judge their subsequent driving behavior.