Modeling And Control Of Free Piston Engine Generator

The development of automobile industry, the increase of car ownership, the deple-tion of oil resources and the environment pollution put forward severe challenges for the traditional automobile industry. Studying and utilizing the energy saving vehicles is the only way to solve the energy and environment problems. Hybrid vehicles as the market-oriented models in the process of pure electric vehicle research has become the focus of automotive development.The selection of Auxiliary Power Unit (APU) in hybrid configuration can be flexible and the free piston engine generator (FPEG) with lots of advantages as small volume, light weight, simple structure and easy maintenance is one of the potential options. FPEG cancels traditional crank linkage and the movement of piston can not to be bounded which make FPEG achieve variable compression ratio and improve fuel economy and fuel Scope. However, FPEG is not widely applied in the real vehicle and one of the key issues is the lack of reliable piston motion control system. The main content of this paper is to study the piston motion control problem for FPEG system.First of all, this paper analyzes the working principle of FPEG and builds a sim-ulation model in AMESim, Its rationality is preliminarily verified through simulation comparison. The model behavior and dynamic characteristics are analyzed by simula-tion which indicates the core control variables that directly impact the system operating performance.Then, piston motion control problem is described as the control of FPE piston clear-ance height at the end of each stroke. A simplified discrete, control-oriented model is built based on the energy conservation equation and the linear quadratic regulator is ap-plied to control the movement position of the piston through controlling fuel injection quantity of injectors. The analysis and validation of the proposed control are verified in AMESim and the simulation results show that performances of the proposed FPEG control method is satisfied but the piston motion transient fluctuation is relatively large when the electromagnetic load suddenly changes.Finally, for this problem of piston motion transient fluctuation, the piston motion control solution based on Reference Governor method is applied to enforce constraints. Newton’s method is exploited for the state prediction because the future state of FPEG can not be explicitly expressed. The analysis and validation of the proposed Reference Governor control method are verified in AMESim and the simulation results show that the Reference Governor control method can cooperate harmoniously with LQR control method which achieves the good performance of piston position tracking and the fluctu-ation constraints enforcement to ensure the stability of FPEG system.This paper provides some ideas for designing FPEG piston motion control system, but some work needs to be done in the future. In general, it is hard to achieve the position of piston movement which needs to be estimated in the future. In addition, This paper does not analyze the boot process of FPEG, the start control needs to be researched in the future.