Energy Management Optimization of Series Hybrid Electric Bus Using an Ultra-Capacitor and Novel Efficiency Improvement Factors

The existing series hybrid electric bus (SHEB) uses an ultra-capacitor (UC) to extend battery life, mitigate vehicle weight, and reduce cost. However, previous studies did not clearly identify the operation timing and load of the UC for efficiency improvement in an SHEB. This paper proposes novel efficiency improvement factors, with their application criteria for the ideal operation timing and load of the UC in an SHEB. The factors are the threshold of the required power of the motor (TRPM), slope of the power split ratio (SPSR), and y-axis intercept of the power split ratio (YPSR). The TRPM determines the duration of using just the battery. The SPSR or YPSR determine the most efficient load ratio between the battery and UC. The criteria for using them are set using particle swarm optimization. Manhattan, Braunschweig, and Orange County driving cycles were used to reflect various road load conditions. The results showed that the proposed factors and their setting criteria guarantee a significant reduction in the fuel consumption and more energy-efficient SHEBs.