Theory And Technology Of Railway Energy Harvesting By Magnetic Levitation Oscillation

With the rapid development of railway,the demand for railway monitoring facilities and sensors is increasing.Harvesting the railway vibration energy induced by the travelling loads of rail transit vehicles offers an alternative solution for powering the rail-side equipments.It not only saves a lot of infrastructure investment,but also helps to save energy and protects the environment.Due to the large-scale nature of railway track structure,the complexity of vehicle-track dynamics,the strict requirements for railway safe operation,and the complicated electromechanical coupling mechanism of the rail-borne energy harvesting devices,the current research has not been systematic.It is therefore necessary to carry out both the theoretical and experimental investigations.Therefore,in this thesis,the author studies the vibration-based railway energy harvesting by magnetic levitation.Theoretical model is established and a rail-borne energy harvesting prototype is developed to solve the power supply problems of the railway monitoring equipment and sensor nodes along the railway.This technology could contribute to building up self-powered wireless sensor networks for safety monitoring of railway track.The thesis is sponsored by the National Natural Science Foundation of China entitled “Basic study on service safety of high-speed railway track”(Grant No.51425804).The main research works include:1.The state of the art of electrostatic,piezoelectric,and electromagnetic energy harvesting technologies have been reviewed.Technical parameters of various energy harvesters such as device types,materials,excitation conditions,response characteristics,power output,and energy efficiency are summarized.The research status of railway energy harvesting is introduced.It is found that the current rail-borne energy harvesters do not fit the vibration characteristics of the rail,which limits their application in the railway industry.This set the main research motivations of this thesis.2.The vibration characteristics of railway track were measured through on-site testing.The dynamic response of railway track under travelling loads of rolling stock is evaluated based on the time history and PSD of rail acceleration signals.It provides basic data for follow-up research.3.The FSC multi-channel digital electro-hydraulic servo fatigue test system was used to simulate the wheel-rail dynamics,and the experimental testing was conducted for describing the characteristics of piezoelectric and electromagnetic energy harvesters.The vibration characteristics of the track under different combinations of wheel-rail interaction force,excitation frequency(representing the running speed of rolling stocks),and vibration displacement amplitude of track structure are studied.The proposed piezoelectric and electromagnetic energy harvester devices were installed on the rail,and the output energy parameters(i.e.output voltage,current,and power)are compared.It is found that the performance of piezoelectric energy harvesting is limited by its physical properties,and the generated current is small;whereas the electromagnetic energy harvester can generate a relatively larger output power in a wider frequency band,which is suitable for applications in the field of rail transit.Therefore,in the subsequent chapters of this thesis,further research on the theory and technology of rail-borne electromagnetic energy harvesting by magnetic levitation is carried out.4.The nonlinear dynamic Duffing equation of the electromagnetic energy harvester is established,and the nonlinear stiffness characteristics of the energy harvester device are studied,which provides a theoretical basis for broadband energy harvesting of railway vibration.The Maxwell stress tensor method is used to calculate the nonlinear magnetic restoring force and nonlinear magnetic stiffness.Analytical solution of nonlinear Duffing equations is derived.The multi-scale solution of the tri-stable Duffing equation for electromagnetic energy harvester is derived.The KB solution of the tri-stable electromagnetic energy harvester with fractional damping is derived.The primary and sub-harmonic resonance responses by KMB asymptotic method are analyzed.The nonlinear dynamic response characteristics of the electromagnetic energy harvester by magnetic levitation oscillation are theoretically obtained.5.A theoretical analysis model of multi-stable nonlinear electromagnetic energy harvesting system is established.The universal nonlinear restoring force and the restoring potential energy of the multi-stable dynamical system are deduced.Based on bifurcation and chaos theory,the mechanism of multi-stable nonlinear electromagnetic energy harvesting is studied,the conditions for entering into high-energy orbits are explored,and the characteristics of dynamic bifurcation and chaotic motion are studied.The phase trajectory,dynamic bifurcation and chaotic motion states of the multi-stable nonlinear electromagnetic energy harvesting system are characterized by the phase diagram,Poincaré section and the largest Lyapunov exponent.6.The structure of multi-stable nonlinear electromagnetic energy harvesting system is designed.The phenomena of dynamic bifurcation,escape from potential well,high-energy orbit oscillation,chaotic motions are experimentally investigated.One quad-stable and two tri-stable electromagnetic energy harvesters by magnetic levitation are presented and verified.The experimental results are analyzed by using phase diagrams,Poincaré section,largest Lyapunov exponent,and bifurcation diagrams.In addition,the stroboscopic sampling algorithm for illustrating bifurcation diagrams is developed and elaborated.This method can intuitively illustrate the complicated motion state of the system.The experimental results indicate that the electromagnetic induction MEH system based on magnetic levitation oscillation can create a multi-stable potential well,which can realize the inter-well oscillation,and thus increase dramatically the output current(i.e.electrical load capability),output power,and operation frequency bandwidth of the energy harvester.7.The overall framework of the railway vibration-electromagnetic coupled dynamic model is established.First of all,the vehicle-track interaction model calculates the transient response of the rail,which is subjected to the traveling load of a vehicle.The calculated response of the rail acceleration is then input to the non-linear oscillation equation as excitation.The non-linear stiffness parameter of the oscillator is calculated by the Maxwell stress tensor.Then,an explicit integration method is used to solve the non-linear differential equation of the magnetic levitation oscillator;the multiple scales technique(a perturbation technique)is used to derive the frequency response of the oscillator.Finally,the system response of the oscillator is input to the electromagnetic coupling equation governed by the Maxwell theory to get the induced voltage.By this way,we can calculate the power generation capability of the rail-mounted magnetic levitation oscillator subjected to the traveling load of the rolling stock.By using 5-2000 Hz DC3200-36 broadband vibration excitation system,the frequency response characteristics and power generation capabilities of the rail-borne electromagnetic energy harvester by magnetic levitation are experimentally investigated.8.Based on micro-electromechanical integration technology in the field of micro-scale energy generation,an electromagnetic energy harvesting prototype is developed.The design and implementation of this prototype are in line with the vibration characteristics of the railway track,the rolling stock gauge,and the safety requirement of railway engineering.The dimension limitation is considered and the miniaturization design methods are implemented.A DC-DC converter is developed to ensure a stable and standard DC output.9.An autonomous wireless monitoring node based on the electromagnetic energy harvesting prototype is proposed.The developed smart nodes include: the electromagnetic energy harvester,MEMS accelerometer,temperature and humidity sensor,lithium battery,microcomputer control module,ZigBee wireless communication module,power management module and control module.The wireless communication performance,power consumption,and immunity performance of the prototype were tested.The proposed self-powered ZigBee node is capable of monitoring railway vibration data(vibration acceleration,etc.)in real time and realizing wireless data transmission.