Electromagnetic Loss Analysis of a Linear Motor System Designed for a Free-Piston Engine Generator

Abstract

A free-piston engine generator is a new type of power generating device, which has the advantages of high efficiency and simple structure. In this paper, a linear motor system composed of a moving-coil linear motor with axial magnetized magnets and a H-bridge pulse-width modulation (PWM) rectifier is designed for portable free-piston engine generators. Based on the finite-element model of the motor and physical model of the rectifier, the combined electromagnetic model is presented and then validated by the prototype-tested results. The electromagnetic processes of the linear motor system are simulated. The electromagnetic losses during the standard working cycle are analyzed. Under the rated reciprocating frequency of 50 Hz and the rated reciprocating stroke of 36 mm, the mechanical-to-electrical energy conversion efficiency of 86.3% can be obtained by the linear motor system, which meets the requirement of portable free-piston engine generators.Electronics 2020, 9, 621 2 of 11 mover assembly moves down from the TTC to BTC driving by the combustion pressure.During the stable running, the linear motor works in generating mode all the time. The electromotive force (EMF) in the coil of the motor is quasi-sine wave, and the generating current in the coil is controlled as standard sine wave by the rectifier, and the electrical energy will be stored in the battery in the form of direct current. During the starting of the device, the linear motor must work briefly in motoring mode to start the motion of the piston-mover assembly.

Electromagnetic Characteristics Analysis of a Tubular Moving Magnet Linear Generator System

“…The tested mover motion is compared with the mover motion simulated by the validated finite element model (FEM). The mover motion curve is designed according to the actual motion of the FPE [17]. As shown in the figure, the time of the stroke is about 14 ms, and the max speed of the mover motion is up to 3.5 m/s.…”

“…Xu [15][16][17] designed a series of tubular single-phase moving coil linear generators for FPEs. This kind of single-phase moving coil linear generator has the advantage of having less moving mass, a faster response, and better controllability, but has the disadvantage of a lower power density.…”

Electromagnetic Engines: A Review

“…The design is simple and straight forward, it has multiple different elements [2], but it mainly focuses on the permanent magnet in the piston. The other elements are the cylinder, connecting rod, flywheel, the battery, and the magnet above the piston that allows it to move up and down.…”

Linear Permanent Magnet Vernier Generators for Wave Energy Applications: Analysis, Challenges, and Opportunities

“…Hence, devices to transform the linear to the rotary motion were eliminated and replaced by linear machines as more profitable alternatives. Linear structures have been broadly employed in different applications such as rail transit systems [3], ropeless elevators [4,5], automatic doors [6], electromagnetic suspension systems [7], free-piston engines [8,9], and wave energy applications [10]. The main scope of this research is to investigate the utilization of linear machines in harvesting wave energy, known as one of the most significant renewable energy resources.…”