Parameter Matching,Modeling And Energy Management Strategy Of Fuel Cell Hybrid Tramway

As the basic industry of our country,the vigorous development of rail transit has a positive and irreplaceable role in promoting economic development and improving people’s livelihood.However,the high energy consumption caused by it cannot be underestimated.Therefore,it is necessary to actively explore the realization of green energy conservation and sustainability in the rail transit industry.Among all the new energy types,hydrogen,as a clean and efficient renewable energy,has been embedded in the strategic development of many countries.Fuel cell(FC)systems,as the main way to use hydrogen energy,has been applied in the fields of distributed power generation,energy storage,and electrified transportation.Due to the slow dynamic response,soft output characteristics,and poor durability,fuel cells are currently combined with energy storage system,such as lithium battery and supercapacitor(SC),to form a hybrid power system to power the vehicles.Taking a fuel cell/battery/supercapacitor hybrid trams as the research object,this thesis focuses on solving the parameter configuration and energy management strategy(EMS)of the hybrid power system.The main research results of this thesis are as follows:(1)The parameter configuration and optimization method of the fuel cell hybrid electric tram on the premise of satisfying dynamic performance are studied in this thesis.First,according to the basic parameters and dynamic performance indexes of fuel cell hybrid electric tramway,the power and energy requirements of typical drive cycles are analyzed.Considering the output characteristics of FC,battery and SC,the applicability of the three power sources to typical operating conditions are studied,which provides a basis for subsequent parameter configuration;based on the above analysis results,a parameter configuration and optimization method is proposed.Then,on the requirement of dynamic performance,the fuel cell parameters and the feasible region of battery and SC pack number are obtained.To achieve higher specific energy and smaller mass and volume for the auxiliary system consisted of batteries and SCs,the nondominated sorting genetic algorithm II(NSGA-II)performs multiobjective optimization to obtain the Pareto frontier and a set of non-dominated solutions is selected as the configuration scheme of the auxiliary power system.Finally,the feasibility of the configuration scheme is verified in terms of acceleration performance,climbing performance and failure emergency.(2)In the thesis,the power system model and the controllable inverter and load model is established,providing the basis for the subsequent energy management methods.Firstly,according to the basic parameters and configured power schemes of the hybrid tramway,the power model consisting of fuel cell mode,lithium battery model,supercapacitor model and DC/DC converters is established.Then,the traction inverter models and the three-phase asynchronous motor models are built as the traction load to replace the current commonly used power load that is simulated by controlled sources.The inverters are controlled by space vector pulse width modulation(SVPWM)method and the motors are controlled using indirect rotor field-oriented vector control method.The established load takes speed curve rather than power as the input variable,which is in accordance with actual situation and allows the operation control.The simulation results prove that the established model possess good dynamic performance.The power system model and the controllable load model together constitute the simulation model of the tramway,and also the semi-physical simulation model is built based on the RTLAB real-time simulator,which lays the foundation for the research in the subsequent chapters.(3)According to the structure and configuration of the fuel cell hybrid electric tramway,the energy management strategy based on off-line global optimization algorithms for the hybrid tramway are studied in the thesis,and the real-time loss of fuel cell system life is considered to explore the optimal economic efficiency.First,a computation efficient multidimensional dynamic programming algorithm(DP)based on vectorization is proposed,which reduces the cycle structure of traditional dynamic programming and greatly improves the computing speed of the method and provides a solution for the global optimization problem of the fuel cell/lithium battery/supercapacitor three-hybrid power system.Secondly,the fuel cell life loss evaluation formula is introduced to convert its real-time life loss into operating costs,and a cost minimization strategy concerning FC degradation and operation cost based on the computation efficient multi-dimensional DP is proposed.The results show that this method can achieve optimal economic performance,and effectively extend the life of the fuel cell system.Then,because of the theoretically similar optimization performance to DP and online application ability,the EMS based on Pontryagin minimum principle(PMP)is widely used on the hybrid system with two power sources.However,the current EMS based on PMP simplifies the co-state variable as a constant,which lead to the poor optimization performance and is not suitable for the hybrid structure with SC.In terms of this issue,the analytical formula of the co-state variables are deduced and a multi-dimensional PMP energy management is proposed in the thesis.Compared with DP,it is demonstrated that by selecting appropriate initial value of the co-states,the proposed method based PMP can achieve global optimization,and the effect is almost equivalent to the dynamic programming method.(4)Based on the established hybrid power system model,an online adaptive energy management strategy is proposed in the thesis.First,considering that the available power of the tramway changes with the SOC of auxiliary system,a speed self-adjusting strategy is designed to adjust the tramway speed actively by calculating the available acceleration speed when the power system cannot provide enough power to maintain the tramway running at the planned speed.Then the closed-loop feedback system eliminates the distance difference before and after the adjustment,ensuring the safe and reliable operation of the tramway.Secondly,the tramway runs at the adjusted speed,and the motor load requests power from the bus.An adaptive voltage-power droop control is adopted to allocate demand power.And adjustment factors are designed based on the SOC of battery and SC to adaptively adjust the droop coefficient to obtain better performance;Finally,the proposed method is carried out on the RTLAB semi-physical platform.The verification results show that this method can effectively reduce hydrogen consumption,maintain SOC stability,control the bus voltage range,and avoid the influence of load power on the design of distribution rules.