| Impact phenomena(such as elevator fall,aircraft landing,artillery recoil,etc.)are inevitable in the areas of daily life,transportation and military equipment.In order to reduce the damage to the equipment and crew caused by the impact,various kinds of buffer absorbers are used to dissipate / absorb impact energy and reduce the transmission rate of impact force.Traditional absorbers generally adopt the hydraulic damping method or the low stiffness deformation element energy absorption method,but their impact force transmission characteristics can only adapt to specific impact conditions,which cannot meet the development needs of related technical fields.Magnetorheological energy absorber(in short MREA)is a controllable absorber that can adjust the flow characteristics of the flowing medium in real time by changing the magnetic induction intensity in the damping channel.Therefore,MREA can adapt to different impact conditions and is an important development direction in the field of impact isolation.The MREA is controlled by the excitation of the electromagnetic coil to control the magnetic induction intensity of the damping channel,which is an inductive load for the excitation current source.In addition,the impact process only takes tens of milliseconds generally,so the rapid response of the excitation current source is a key factor for real-time control of the MREA.In this thesis,aiming at the specific inductive load,an excitation current source based on the synergy between supercapacitor and Buck converter is proposed,which has the characteristics of wide output range and fast response speed.The main contents of this thesis are as follows:The development of MREA and excitation current source at home and abroad are summarized respectively.The necessity of real-time control of buffer force and design of high-speed current source are pointed out.The disability of existing high-speed current sources to meet the requirements of MREA to achieve effective impact isolation is analyzed,the research content and academic significance of this thesis are put forward.The working principles of MREA are described in detail,and the rheological parameters of magnetorheological fluid are identified.The static magnetic field finite element simulation of MREA is carried out by Maxwell software to obtain the relationship between current and magnetic field.Considering the inertial force and minor losses,the establishment of the dynamic model based on parallel plate model is described,and the functions expression of buffer force.The dynamic characteristics and controllability of MREA under impact load are simulated by Matlab,and finally the index requirements such as response time and output range were proposed for current source.A high-speed current source based on the synergy between supercapacitor and Buck converter for MREA is proposed.A control strategy is put forward,which uses the supercapacitor with high initial voltage to raise the current quickly and the Buck converter to maintain the expected current.The equivalent circuit model of MREA is proposed,and a circuit model of the supercapacitor is established.Then,the state-space averaging principle is employed to obtain the small-signal circuit model of the Buck converter under nonideal condition.Simulation of current dynamic characteristics is carried out by Matlab and Saber software,which verifies the correctness of the model and the effectiveness of the control strategy.Both hardware and software part are designed in detail with STM32 microcomputer as the control core.In the hardware part,the supercapacitor circuit,Buck converter circuit,voltage and current sampling circuit and auxiliary power supply circuit are designed,and the parameter calculation and selection of electronic components are analyzed.As for software part,the main program,interrupt subprogram and incremental PID control algorithm are designed.Finally,the current source prototype is made after completing PCB design.Taking the actual MREA as the load of current source(the equivalent resistance and inductance of MREA are1.3 Ωand 25 m H respectively),a series of tests are carried out.The results show that the current source has great linearity and reliability,the output range of the current source is continuously adjustable from 0 to 9 A,and the response time is no more than 1.88 ms,which meets the index requirements very well.Finally,a drop tower facility is set up to carry out a series of impact tests on the MREA under constant current and variable current at different impact heights.The impact test results show that the MREA achieves great buffer effect,and the test results are in good agreement with that of simulation. |
