Research On Internal Combustion-Linear Generator Integrated Power System And Its Implementation

Free-piston linear generators are under investigation by a number of research groups worldwide for their potential advantages, such as compact structure, good fuel adaptability and high efficiency. Only two-stroke cycles ware used by reported free-piston linear generators up to now, but the energy efficiency of two-stroke engines is still significantly lower than four-stroke engines, and two-stroke engines are eliminated by modern vehicles. In order to use energy more efficient and clean, a novel four-stroke free-piston linear generators was proposed. The major contributions of this paper were as follows:(1) A novel internal combustion linear generator integrated power system was proposed. The four-stroke cycles used by the system was presented. Dynamics simulation model of the system was created, and the simulation was done based on the given parameters of a virtual prototype. The dynamic variations of displacement, velocity and pressure in the cylinder were given out. The influence of parameters on the dynamic characteristics of the system was analyzed. The energy conversion and transfer process of the system was revealed. The preliminary prediction of the system performance was predicted. Simulation models can be used as design basis for the system and its key components.(2) To achieve the required high generating efficiency, low moving mass, and high thrust linearity, a novel moving coil PM linear generator was proposed. An equivalent magnetic circuit model of the generator was presented. The calculation formulas for electromagnetic force, the armature inductance and generating efficiency of the generator were deduced. The main structure parameters of the generator were optimized. Combined with the finite element analysis, thrust and power characteristics of the generator were calculated. Aiming at the displacement measurement, a non-contact displacement measurement system based on the magnetoresistive principle was presented.(3) Based on the designed moving coil PM linear generator, a novel four-quadrant controlled DC power supply was proposed to aim at the corrent control. Working process of the proposed power supply was presented. To ensure continuous current in the generator armature and minimize the switch loss in the IGBT, the determination method for the PWM frequency was given out. Dynamics simulation models of the system were created based on the SimPowerSystems. Combined with the simulation model of the system, four-quadrant working processes were simulated. Special attention was paid on the fluctuation range in the corrent and the energy flow between the two ultracapacitors.(4) A 4kN permanent magnet linear generator prototype was developed. A thrust test rig was built. The thrust-displacement characteristics and the thrust-current characteristics of the generator prototype were measured. The experiment results and the analysis results were validated. Hardware systems of the proposed four-quadrant controlled DC power supply were created. The control procedures were prepared. The four-quadrant working processes ware tested by using the developed permanent magnet linear generator prototype as the control object. Experiment results ware presented in this paperfor verification(5) The main interference factors of the free-piston reciprocating motion were analyzed. The active control necessity of the free-piston reciprocating motion were argued. Based on using electromagnetic force to control the free-piston movement rules, the control scheme was created. The motion trajectory defined by the four target stroke endpoints was presented. A motion controller based on changing the working states of the linear generator was proposed. Bang-Bang control rules and iterative learning control strategy for changing the working states of the linear generator were prsented. The simulation model was created based on hybrid states. The motion control process of the system was simulated.(6) An experimental prototype of the proposed internal combustion linear generator integrated power system was fabricated and tested. Stable running of the prototype was realized. The generating efficiency of 32%has been obtained up to now. The feasibility and performance of the proposed design were verified. Detailed testing results from the continuous running prototype were analyzed for giving insight into the performance and dynamic behaviors of the novel power system. Based on the simulation model of the system and the experiment results, the thermodynamics parameters of the prototype were investigated by using regression analysis. The main reasons for the difference between the prototype experiment results and the simulation results were revealed.