An economic power regulation strategy for dual-spool turboshaft power unit based on power flow splitting, shaft speed, and variable power turbine guide vanes

Flying cars meet both ground driving and aerial flight requirements, which adds considerable complexity to the design of power systems. A hybrid electric propulsion system (HEPS) based on turboshaft power unit (TPU) offers a promising solution for achieving high power-to-weight ratio and extended endurance. However, the specific fuel consumption (SFC) of turboshaft engine remains relatively high across the full power range, especially under partial load conditions during ground driving. To address this issue, this paper proposes an economic optimal power regulation strategy named Economic-Speed-Angle-Splitting (E-SAS) for TPUs. The strategy leverages the adjustable characteristics of shaft speed, power turbine guide vane angle, and electric power split to enhance fuel economy. First, considering the unique architecture of a variable-cycle dual-spool TPU, a co-working balance equation is developed based on the dual-spool and dual-motor configuration, incorporating motor efficiency improvements. Second, based on this improved balance model, the effects of the three controllable variables on engine performance—particularly on fuel consumption characteristics—are quantitatively analyzed. Then, to derive the E-SAS within defined safety constraints, a hierarchical optimization framework is established, employing a Newton-Raphson-based optimizer (NRBO), the superiority of which is statistically validated against traditional algorithms. Finally, the effectiveness of the E-SAS strategy in reducing fuel consumption is evaluated, and the underlying mechanisms and parameter merit orders are analyzed. Comparative results demonstrate that the E-SAS strategy delivers fuel economy benefits across the full power range, achieving up to 9.67% fuel savings at low power levels. Furthermore, environmental sensitivity analysis confirms the strategy's high robustness across various altitudes, showing great potential for extending the range of flying cars.