Comparative study and optimal design of alternative PM configuration transverse flux linear machine

This paper presents the comparative study and optimal design of a transverse flux linear machine with different PM configurations, viz. surface-mounted and consequent-pole, in which the consequent-pole version is firstly proposed. Firstly, the effect of variation of the main design parameters on both topologies are studied. Then, the multi-objective optimization method based on genetic algorithm combined with response surface methodology (RSM) is adopted to realize the optimal design of these two topologies and Pareto front solutions will be obtained. Finally, the characteristics of these two topologies are analyzed and compared, with particular regard to the advantages and disadvantages of the consequent pole topology

Design and Optimization of Dynamic System for a One-kW Free Piston Linear Engine Alternator-GENSETS Program

In power/energy systems, free-piston linear machines are referred to as a mechanism where the constrained crank motion is eliminated and replaced with free reciprocating piston motion. Depending on the application, the piston motion can be converted into other types of energy and includes compressed air/fluid, electricity, and high temperature/pressure gas. A research group at West Virginia University developed a free-piston linear engine alternator (LEA) in 1998 and have achieved significant accomplishment in the performance enhancement of the LEAs to date. The present LEA design incorporates flexure springs as energy restoration components and as bearing supports. The advantages of using flexure springs are threefold and include: (1) it increases the LEA’s stiffness and resonant frequency, and hence the power density; (2) it eliminates the need for rotary or linear bearings and lubrication system; and (3) it reduces the overall frictional contact area in the translator assembly which improves the durability. The current research focuses on the design and optimization of the flexure springs as the system’s resonant dominating component for a 1 kW free-piston LEA. First, the flexure springs were characterized according to the LEA’s target outputs and dimensional limitations. The finite element method (FEM) was used to analyze the stress/strain, different modes of deformation, and fatigue life of a range of flexure spring designs under dynamic loadings. Primary geometric design variables included the number of arms, inside and outside diameter, thickness, and arm’s length. To find the near-optimum designs, a machine learning algorithm incorporating the FEM results was used in order to find the sensitivity of the target outputs to the geometrical parameters. From the results, design charts were extracted as a guideline to flexure spring selection for a range of operations. Then, methods were introduced, investigated, and analyzed to improve the overall energy conversion performance and service life of the flexure springs and the overall LEA system. These included: a transient FE tool used for fatigue analysis to quantify the life and factors of safety of the flexure springs as well as the spring’s hysteresis; a fluid/structure interaction model used to quantify the energy loss due to drag force applied on the flexures’ side surfaces; packaging of multiple flexures to increase the overall stiffness and to reduce the vibration-induced stresses on flexure arms due to higher harmonics; a model to investigate the two-way interactions of the flexures’ dynamics with the alternator and engine components to find an optimum selection of the LEA’s assembly; a non-linear friction analysis to identify/quantify the energy losses due to the friction of the sliding surfaces of the flexures and spacers; and a series of static and transient experiment to determine the non-linearity of flexures’ stiffness and comparison to FEM results and for validation of the energy audit results from numerical and analytical calculations. With over 6000 flexure designs evaluated using artificial intelligent methods, the maximum achievable resonant frequency of a single flexure spring for a 1 kW LEA was found to be around 150 Hz. From the FEM results, it was found that under dynamic conditions the stress levels to be as high as twice the maximum stress under static (or very low speed) conditions. Modifications of the arm’s end shape and implementation of a shape factor were found as effective methods to reduce the maximum stress by 20%. The modal analysis showed that the most damaging modes of deformations of a flexure spring were the second to fourth modes, depending on the number of arms and symmetry of the design. Experiment and FEM results showed that using bolted packaging of the springs can damp a portion of the vibration and improve the performance. The drag force loss was found to account for 10-15% of the mechanical losses in a 100 Wnet LEA prototype. From the manufacturing perspective, use of water jet was found the most economical method for manufacturing the flexures which could make the commercial production of the LEAs feasible; however, for high-efficiency, high-durability machines, additional material treatments, and alternative manufacturing methods are essential

Analysis and Optimization of a Dual Free Piston, Spring Assisted, Linear Engine Generator

The free piston linear engine (FPLE) generator has the potential to displace existing crankshaft driven engine technology because of its relative simplicity, higher efficiency, and increased power density. Continued interest in hybrid-electric vehicles for transportation and tightening emissions regulations has created a challenging market for conventional piston engines. Combined with rising market interest in localized power generation means there are exciting opportunities for innovative technologies that can satisfy both regulatory and commercial demands. Many groups around the world are currently working to advance the state of the FPLE, and recent success at West Virginia University will lead to a working prototype device within the next three years.;This dissertation presents the analysis and optimization of a dual free piston, spring assisted, linear engine generator (SALEG). The primary moving part is a dual piston translator driven by 2-stroke homogeneous charge compression ignition combustion cycles such that the compression stroke for one cylinder corresponds to the expansion stroke of the other. The dynamics of the translator are augmented by the addition of springs that support higher frequency operation, provide energy storage to support cyclic stability, and can be tailored to achieve a desired translator dynamic profile. Current challenges for the device involve optimization for high efficiency performance at steady state and control of the translator position and combustion events.;Using numeric simulation tools in MATLABRTM and Simulink, the dynamic behavior of the translator is modeled in conjunction with the in-cylinder thermodynamics for each engine cylinder and the linear electric alternator load. Sweeps of the primary design parameters explore the design space while demonstrating the interdependency that is characteristic of the FPLE. Then, a genetic algorithm is employed to optimize the SALEG for efficiency based on target power and practical operating constraints. It is demonstrated that low maximum stroke to bore ratio and low intake temperature are favored. Also, the design space becomes more restrictive as target power is raised, but for a range of devices as high as 25 kW, efficiency greater than 40% can be achieved.;Control mechanisms for the simulated SALEG are demonstrated and compared. These entail the control of alternator force, engine fueling, and intake conditions through the use of proportional and integral control methods. The control methods are applied to achieve resonant start-up of the device and to respond to changes in load demand and misfire. Motored, resonant hot-start is simulated for a device with natural frequency of 40 Hz, and the linear motor and controller parameters are tested. Misfire is shown to lead to rapid loss of compression, so the motored resonant control mechanism is employed to recover after misfire. A map-based controller is used to control intake temperature in response to rapid change in load. For a 50% reduction in load, intake temperature is raised by 15% (40 °C) and results in an efficiency drop from 38% to 22% at steady state. Ultimately, the simulation tool represents a platform for future investigations where experimental data and more sophisticated modeling techniques might be included to enhance the research and advancement of the free piston linear engine