Abstract
Free-piston linear generators (FPLGs) have attractive application prospects for hybrid electric vehicles (HEVs) owing to their high-efficiency, low-emissions and multi-fuel flexibility. In order to achieve long-term stable operation, the hybrid system design and full-cycle operation strategy are essential factors that should be considered. A 25 kW FPLG consisting of an internal combustion engine (ICE), a linear electric machine (LEM) and a gas spring (GS) is designed. To improve the power density and generating efficiency, the LEM is assembled with two modular flat-type double-sided PM LEM units, which sandwich a common moving-magnet plate supported by a middle keel beam and bilateral slide guide rails to enhance the stiffness of the moving plate. For the convenience of operation processes analysis, the coupling hybrid system is modeled mathematically and a full cycle simulation model is established. Top-level systemic control strategies including the starting, stable operating, fault recovering and stopping strategies are analyzed and discussed. The analysis results validate that the system can run stably and robustly with the proposed full cycle operation strategy. The effective electric output power can reach 26.36 kW with an overall system efficiency of 36.32%.
Highlights
Free-piston linear generators (FPLGs) are believed to be promising alternative hybrid power systems for hybrid electric vehicles (HEVs) due to their potential advantages of high-efficiency, low emissions and various fuel flexibility [1,2,3]
The force distribution of the system can be briefly illustrated in Figure 2, in which the zero reference is set at the starting position of the top dead center (TDC) and the positive direction is from
The force distribution of the system can be briefly illustrated in Figure 2, in which the zero reference is set at the starting position of the top dead center (TDC) and the positive direction is from functions a motor and drives the piston towards bottom dead center (BDC)
Summary
Free-piston linear generators (FPLGs) are believed to be promising alternative hybrid power systems for hybrid electric vehicles (HEVs) due to their potential advantages of high-efficiency, low emissions and various fuel flexibility [1,2,3]. The development status of these prototypes indicates that the single-cylinder FPLG has advantages of a simple structure and easy system control, and thereby is intensively studied [14,15] Several institutions such as the German Aerospace Centre (DLR), Toyota Central R&D Labs., Inc., and the Nanjing University of Science and Technology (NUST), have designed and developed. The combustion parameters and engine performances such as the combustion duration, the spark timing, the indicated mean effective pressure and the mass fraction burned were analyzed using a numerical Matlab/Simulink model Some detailed factors such as the heat transfer, the enthalpy of the intake and exhaust air, the gas leakage and the friction loss were not considered into their model [9].
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