| With the advantages of large carrying capacity,short construction period,attractive appearance and low cost,modern trams have been developed in many cities in China.Wireless power transfer(WPT)technology avoids the physical contact of power supply wires,it has the advantages of safety,reliability and flexible power supply.Hybrid energy storage systern(HESS)has advantages of both the high power density of supercapacitors and the high energy density of batteries.In order to take advantage of WPT technology and HESS,this paper proposes to combine the both technology as a new power supply mode for modern trams.WPT technology can supply power for vehicles by static and dynamic mode.Static WPT system can supply power for HESS when the vehicle stops.Dynamic WPT system can supply power for HESS during the driving process and prolong the power supply time.In order to improve the power supply performance of WPT system for HESS,this paper focuses on the research of energy efficiency optimization of hybrid energy storage modern tram WPT technology.The control strategy of WPT system for HESS load,the optimization of coupling mechanism of dynamic WPT system,and the multi-variable optimization of each link of WPT system are studied,and the research points are verified by simulation and experiment.The control strategy of WPT system is usually designed for a single energy storage load,and HESS is seldom considered.In order to ensure the high efficiency of WPT system and the power supply requirement of energy storage system,the system control method needs closed-loop control on both transmitting side and receiving side,which is difficult to guarantee the reliability of control.In this paper,a WPT system with HESS load is proposed.Based on the two-port network method,a mathematical model of the system is established.It is found that there exists an optimal power to make the WPT system achieve the highest efficiency through the analysis of system characteristics.In order to make the WPT system work at the highest efficiency,this paper proposes an optimal efficiency tracking control method based on dynamic power regulation by optimizing the power allocation strategy of HESS,so that the HESS load can be maintained at the optimal power,thus ensuring the optimal efficiency of the WPT system.At the same time,considering the difference of running state of modern tram,which makes the initial voltage of HESS charging different,an optimal efficiency tracking control method based on dynamic power regulation is proposed,the method only controls the DC/DC converter on the receiving side in a closed loop way,which improves the reliability of the control.The difficulty of dynamic WPT technology lies in the scheme design and switching strategy of coupling mechanism.The typical scheme of coupling mechanism is long transmitting coil-short receiving coil mode,which has weak coupling interval and unstable output characteristics.Existing switching strategies usually require additional sensors,which increases the cost of system design.Aiming at the characteristics of body length of modern tram,this paper proposes an improved short transmitting coil-long receiving coil mode,which can ensure the stability of system output and effectively reduce the eddy current loss under the vehicle.To solve the problem of switching coupling mechanism in mobile process,this paper proposes a method based on electrical parameter identification to detect the coil position and select the output voltage as the switching index to realize the switching of coupling mechanism.This method only needs to use the existing voltage sensors.In order to further optimize the performance of the coupling mechanism,this paper also proposes to use genetic algorithm to optimize the geometric parameters of the coupling mechanism,so as to reduce the loss and cost of the coupling mechanism.The parameter optimization of WPT system usually only considers the constraints of electrical parameters such as power and efficiency,seldom combines with vehicle operation conditions,and only considers WPT system in parameter design,without joint load optimization.Based on the operation conditions of modern trams,an intermittent WPT power supply mode is proposed in this paper.This mode can balance the energy consumption of HESS in each operation section of the vehicle and contribute to the capacity allocation of HESS.In this paper,the traction calculation model of modern tram and HESS electrical characteristics are established,and the power and energy changes during the operation of the vehicle are analyzed.It is found that the capacity allocation of HESS and the power level of WPT are affected by the line conditions.A multi-variable optimization method for energy efficiency optimization is proposed.The capacity allocation of HESS,the power level of WPT system and the geometric parameters of coupling mechanism are optimized,and the optimization process is designed.The advantages of intermittent WPT power supply mode in reducing power level of WPT system,balancing energy consumption in operation zone and reducing load capacity allocation of hybrid energy storage are illustrated through the case study of Wuhan East Lake Line.In order to verify the research content of this paper,a 50 kW high-power WPT system and a HESS experimental platform with the same power level are built to realize the joint operation.The cooperative control strategy of power and efficiency of WPT system based on HESS load is validated on the experimental platform.Dynamic WPT power supply is realized by improving the coupling mechanism.The advantages of power supply characteristics and the feasibility of switching strategy of the improved coupling mechanism are verified. |
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