Research On Design And Control Of Central Combustion Internal Combustion Linear Generator

The central combustion type internal combustion linear generator is composed of a central combustion chamber,dual linear generators and dual gas springs.These coponents are arranged symmetrically in the horizontal direction.It has the advantages of simple structure,dynamic balance,variable compression ratio,wide fuel adaptability and high conversion efficiency.However,due to the cancellation of the mechanical constraints of the crankshaft connecting rod,the output performance of the system is completely nonlinearly coupled by the external characteristics of the combustion chamber,linear generator and gas spring.The combustion process is prone to conditions such as misfire,insufficient combustion,and deflagration,which introduce cyclic fluctuations and make it difficult to achieve long-term stable operation due to the inconsistency of the periodic motion of the piston.In addition,the linear generator operates in the condition of reciprocating acceleration and deceleration and variable load,and needs to precisely coordinate and control the combustion parameters,which puts forward new requirements for the efficiency,dynamic response and controllability of the motor system.Therefore,in this dissertation,the following researches are carried out for the matching design of nonlinear coupled system,high-performance linear motor design,system integration and stability control:1)Research on modeling and matching design of nonlinear coupled systems.Based on the distribution characteristics of the thermodynamic process of the internal combustion engine and the gas spring in the position domain,and the voltage equations of the linear motor’s electric and power generation process,a nonlinear coupled system model of the central combustion chamber type internal combustion linear generator is established.The influence of variables such as mover mass,piston stroke,gas spring cylinder diameter,and compression ratio on the performance of the system,such as output electrical power,mechanical loss,and efficiency,are explored.It is clear that the system has the characteristics of slow compression speed and fast expansion speed,which is beneficial to improve the scavenging efficiency and reduce the combustion heat loss.Finally,based on the energy balance relationship in the stroke,the structural parameters and performance indicators of the system components are matched and designed,which provides a theoretical basis for prototype development and system integration.2)Design and research of high-efficiency and high-dynamic-response linear generator.Based on the system stiffness,resonant frequency,and the requirements of high thrust-to-mover mass ratio and high efficiency of linear motors,a double-sided short stators and long mover topology is proposed.A double-linked Halbach permanent magnet array is designed,and non-magnetically conductive lightweight materials are introduced to explore the effects of different magnetic circuit structures and magnet thicknesses on the air-gap magnetic flux density.Aiming at the reciprocating acceleration,deceleration and variable load characteristics of linear generators,the influence of slot height on motor loss and efficiency is studied,and a motor efficiency optimization method based on the matching of motor efficiency spectrum and operating conditions is proposed.After testing,the following performances of the developed prototype are obtained: a maximum thrust of 1000 N,a mover weight of 2 kg,an acceleration greater than 30 g,an operating frequency of up to 45 Hz,a peak power of2.39 k W,and a peak electromagnetic braking efficiency of 94.5 %.3)Research on the detent force modeling and weakening method of the doublesided flat linear motor.Aiming at the inconsistency of the current linear motor cogging effect and end effect solution method and the complicated process,by studying the distribution characteristics of the magnetic potential in the position domain,a mathematical model of the linear motor detent force with the virtual magnetic pole/slot sub-domain is proposed.The magnetic field distribution and positioning force of the long/short mover linear motor are solved accurately.In addition,based on the Fourier series,the resultant forces model of the cogging force and the end force are deduced,and the formation and weakening principle of the detent force in linear motor are revealed.The detent force weakening method based on single-slot shape adjustment,multi-slot amplitude modulation,and phase modulation of edge force and cogging force is proposed,and a low detent force double-sided linear motor with different widths of end slots and teeth is designed.After testing,the thrust ripple of the developed linear motor is less than 1.5%,and the decrease rate of the detent force compared with the initial structure reaches 95.5%.4)Prototype system integration and control system design research.Based on the developed central combustion chamber,linear motors and gas springs,the prototype system is gradually integrated,and the established mathematical model is verified.The coupling mechanism of the central combustion type internal combustion linear generator is clarified.The key factors affecting the long-term continuous and stable operation of the system are discussed,and a dual-motor master-slave synchronous control method based on reference current feedforward,piston and speed tracking is designed,and a stable control method based on energy balance between dead center positions is designed to achieve the target of the top dead center position error less than±0.2 mm in combustion fluctuation and misfire conditions.Finally,relevant experimental research is carried out based on the built electromechanical system platform,which verifies the effectiveness of the control algorithm and realizes more than 1000 continuous ignition operations.