Novel hybrid power system and energy management strategy for locomotives

The traditional fuel locomotive is the primary type of locomotive currently in operation on non-electrified railways; however, it presents certain disadvantages including a low efficiency and high fuel consumption. Therefore, in this study, a multimode hybrid locomotive configuration scheme is designed to improve the system efficiency and reduce fuel consumption during locomotive operation; further, the power flow state under different modes is analyzed, the mathematical model of the hybrid locomotive is established, and a system optimal efficiency calculation method is developed. Moreover, an energy management strategy based on the optimal system efficiency and with a hierarchical architecture is proposed. In the upper layer of this proposed energy management strategy, the optimal efficiency of all operating points and operational state of each component are determined offline using the optimal efficiency calculation method. The lower layer selects and coordinates the mode online by identifying the condition of the wheel and distributes the torque of each power source and the state of each transmission system component. The simulation results indicate that the fuel economy of the proposed energy management strategy is improved by 27.22% compared with that of the traditional fuel locomotive, and the fuel economy is only 7.21% lower than the global optimization result obtained via dynamic programming. In addition, no frequent clutch switching is observed under this strategy, and the electric motor does not operate under non-rated conditions for prolonged periods; these advantages ensure the rationality of control and the reliability of component operation. Finally, the results of a hardware-in-theloop simulation test confirm that the proposed energy management strategy demonstrates good real-time performance.