Feasibility of Multiple Piston Motion Control Approaches in a Free Piston Engine Generator

Mehar Bade; Nigel Clark; Parviz FamouriPriyaankaDevi Guggilapu

摘要

The control and design optimization of a Free Piston Engine Generator (FPEG) has been found to be difficult as each independent variable changes the piston dynamics with respect to time. These dynamics, in turn, alter the generator and engine response to other governing variables. As a result, the FPEG system requires an energy balance control algorithm such that the cumulative energy delivered by the engine is equal to the cumulative energy taken by the generator for stable operation. The main objective of this control algorithm is to match the power generated by the engine to the power demanded by the generator. In a conventional crankshaft engine, this energy balance control is similar to the use of a governor and a flywheel to control the rotational speed. In general, if the generator consumes more energy in a cycle than the engine provides, the system moves towards a stall. If the generator consumes less energy, then the effective stroke, compression ratio and maximum translator velocity must rise steadily from cycle-to-cycle until the heat transfer losses stop the increase. Moreover, when stiff springs are added to the FPEG system, the dynamics becomes more sinusoidal and more consistent with increasing spring stiffness. To understand the behavior of proposed control and cycle-to-cycle variations, a comprehensive FPEG numerical model with a 1 kW target electric power was developed in MATLAB/Simulink. An FPEG system corresponding to that numerical model has been operated in the laboratory. This MATLAB/Simulink numerical model has been used to examine the sensitivity of FPEG dynamics and performance parameters to the changes in design and operating inputs. A difficulty during the modeling is associated with the cycleto-cycle energy balance, and this difficulty is also reflected in the real-world FPEG control. Therefore, the authors have devised a control strategy similar to the real world intended control methodology. In this numerical model, two different feedback control methodologies were implemented and investigated. These control methodologies were applied to regulate the generator load with selected control or input variables, namely peak pressure, mid-stroke piston velocity, trapped compression ratio and dead center set points. The controllers with optimized coefficients demonstrated the feasibility of energy balance management during the transient operation. Based on the simulation results, the controllers with compression ratio, peak pressure and dead center clearance set points as control variables demonstrated stable FPEG operation whereas the mid-stroke velocity failed to achieve the steadystate operation due to deviation in the piston dynamics. The simulation results from this study will be used as the pathway for improving and optimizing the experimental FPEG design.

机译：由于每个独立变量都会改变时间相对于时间，因此发现了自由活塞发动机生成器（FPEG）的控制和设计优化非常困难。这些动态反过来改变了发电机和引擎响应对其他管理变量。结果，FPEG系统需要一种能量平衡控制算法，以便发动机传递的累积能量等于发电机为稳定操作所采取的累积能量。该控制算法的主要目的是将发动机生成的功率与发电机所需的功率匹配。在常规的曲轴发动机中，这种能量平衡控制类似于使用调速器和飞轮控制旋转速度的使用。通常，如果发电机在周期中消耗的能量比发动机提供的能量更多，则系统将朝摊位移动。如果发电机消耗较少的能量，则有效的中风，压缩比和最大翻译器速度必须从周期到周期稳定上升，直到传热损失阻止增加。此外，当将僵硬的弹簧添加到FPEG系统中时，动力学将变得更加正弦，并且与弹簧刚度的增加更加一致。为了了解提出的控制和周期变化的行为，在MATLAB/SIMULINK中开发了具有1 kW目标电力的全面FPEG数值模型。与该数值模型相对应的FPEG系统已在实验室中运行。该MATLAB/SIMULINK数值模型已用于检查FPEG动力学和性能参数对设计和操作输入变化的灵敏度。建模过程中的困难与环周期能量平衡有关，并且在现实世界中的FPEG控制中也反映了这种困难。因此，作者制定了一种与现实世界预期的控制方法相似的控制策略。在此数值模型中，实施并研究了两种不同的反馈控制方法。应用这些控制方法来调节具有选定的控制或输入变量的发电机负载，即峰值压力，中风活塞速度，捕获的压缩比和死亡中心设定点。具有优化系数的控制器证明了瞬态操作过程中能量平衡管理的可行性。基于仿真结果，随着控制变量的压缩比，峰值压力和死亡中心清除点的控制器显示出稳定的FPEG操作，而中风速度无法实现由于活塞动力学的偏差而无法实现稳态操作。这项研究的仿真结果将用作改善和优化实验FPEG设计的途径。

Feasibility of Multiple Piston Motion Control Approaches in a Free Piston Engine Generator

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