Electromechanical state stability evaluation method of series hybrid electric powertrain for heavy vehicle

An evaluation methodology for electromechanical state stability was investigated to ensure the safe and stable operation of a heavy-duty vehicle with Series Hybrid Electric Powertrain (S-HEP). Eight dynamic indices were proposed based on the mechanical and electrical characteristics of S-HEP, including engine-generator torque coordination and energy supply coordination between primary and secondary power sources. The weights of evaluation indices were determined to achieve multi-index integration by using the analytic hierarchy process. A fuzzy comprehensive evaluation method was designed by combining fuzzy theory. The method mapped subjective fuzzy evaluations into quantitative scores through membership functions. The electromechanical state stabilities of a vehicle data were evaluated by using real-world tests under 11 working conditions. The results show that the comprehensive scores of a vehicle are 1.11, 2.45, 3.13, and 3.6, respectively for the low-speed (with an average speed being 18 km/h) constant velocity condition. the high-speed (73 km/h) constant velocity condition, the medium-speed (0~40 km/h) cyclic condition, and the sharp acceleration condition (0~40 km/h). These results demonstrate the effectiveness and repeatability of the proposed method. The evaluation outcome can quantify the level of electromechanical state stability of the system.