Energy Management And Coordinated Control Method Of Fuel Cell Hybrid Power System For Rail Transit

With the “emission peak” and “carbon neutrality” national goals put forward,renewable energy such as hydrogen energy will be further developed and utilized.Hydrogen fuel cell(FC)is a kind of power generation device that uses hydrogen as fuel.It has the advantages of high efficiency,zero pollution,low noise,etc.,and has great development potential.Besides,with the continuous advancement of economic development and urbanization,the country has paid more and more attention to the development of rail transit vehicles.Therefore,applying FC power generation technology to rail transit systems and constructing a green and environmentally friendly hybrid power system for locomotives is considered to be a solution with important practical significance.This thesis takes the FC hybrid power system for rail transit vehicles as the research object.This thesis focuses on the experimental research on the FC coordinated control and power distribution methods of the single-stack/multi-stack hybrid power system,and builds the corresponding hybrid power system hardware-in-the-loop(HIL)simulation platform and physical scale experiment platform to verify the proposed method.The main research results of this thesis are as follows:(1)A HIL semi-physical simulation platform for single-stack hybrid power system and multi-stack hybrid power system is built based on the OP5600 real-time simulator to verify and analyze the research object.The platform consists of OP5600 real-time simulator,RTLAB simulation development software,peripheral signal generation/conditioning circuit,DSP controller,and a hybrid power system simulation model based on Matlab/Simulink.The established simulation model includes power batteries,DC/DC converters,FC power generation equipments,and DC load.In addition,in order to further test the actual effect of the proposed methods,corresponding physical scale experiment platforms are built on the basis of the above-mentioned semi-physical simulation systems.The physical systems mainly include lithium batteries,FCs,DC/DC converters,core control units,and sampling and conditioning peripheral hardware circuits.(2)The FC power generation system is easily affected by factors such as the operating environment,which makes it difficult to estimate the maximum operating point of its efficiency.Therefore,this thesis proposes a FC system maximum efficiency point tracking method based on online identification algorithm.This method establishes a mathematical model of system operating efficiency by analyzing system power generation characteristics and adopting high-order nonlinear functions.In addition,aiming at the problem of slow timevarying parameters in the system,based on the principle of nonlinear curve fitting,the Forgetting Factor Recursive Least Square(FFRLS)algorithm is used to update the model parameters in real time,and the real-time running data and weighting factor are used to improve the estimation accuracy and speed up the response speed of the algorithm.(3)Considering that taking into account the influence of the operating environment on the FC generation efficiency in the energy management method of the FC hybrid system can further improve system performance indicators,this thesis proposes a hybrid energy management method based on efficiency range optimization.By studying the output characteristics of the FC system and combining the parameter identification method,this method divides the “efficiency optimal operating area” for the power generation system,and adjusts the added penalty factor according to the real-time updated area boundary values to improve the operating efficiency of the system.In order to prove the superiority and practicability of the proposed method,the performance comparison and analysis with other power distribution methods are carried out on the built HIL simulation platform and the physical scale down experiment platform.(4)Aiming at the optimization problem of power distribution in the FC hybrid power system,in order to minimize the equivalent hydrogen consumption of the hybrid system and improve the durability of the stack,an energy management method that considers the lifetime loss and the optimal fuel consumption economy is proposed.This method analyzes the impact of the four operating modes of start-stop,acceleration,idling,and braking on the durability of the stack,and studies the coupling relationship between stack life loss and output power,and converts the life loss problem into a system cost minimization problem.Based on the equivalent hydrogen consumption theory,a cost function with the goal of optimal system economy is formulated.In addition,Sequential Quadratic Programming(SQP)algorithm is used to solve the above objective function to determine the reference output power of each power source.Finally,the optimization effect of the proposed method is verified on the builtup physical scale experiment platform,and compared with the dynamic programming method.(5)Aiming at the problem that multi-stack FC systems will cause inconsistent operating states of each stack under different operating environments,thereby accelerating performance degradation and shortening the service life of the entire system,this thesis proposes a multistack FC system coordinated control method based on voltage consistency.This method establishes a semi-empirical degradation model of the stack performance by studying the mapping relationship between the output characteristic curve of the stack and its service time.Secondly,in order to facilitate system expansion and realize the “plug and play” function,a droop control algorithm based on virtual resistance is adopted,and an adjustment factor is designed to adaptively adjust the virtual resistance according to the operating state of each stack to realize load power distribution.In order to verify the effectiveness of the proposed method,simulation verification is carried out on the semi-physical simulation platform built.(6)Taking the multi-stack FC hybrid power system as the research object,in order to ensure the safe and stable operation of the multi-source system and the reasonable distribution of power,this thesis proposes an adaptive hierarchical energy management method for multistack hybrid power system.The method is composed of two links: bottom-level parameter identification and top-level power adaptive allocation.In the bottom-level parameter identification,the Kalman filter algorithm and the FFRLS algorithm are used to estimate the degree of FC performance degradation and identify index model parameters to determine the efficiency optimal operating point of FC system.In the top-level power adaptive allocation,in order to optimize the output power of each power source and ensure the stable operation of the system,based on the results of the lower-level identification,this thesis formulates an objective function related to the State of Charge(SOC)of the power battery,the hydrogen consumption of the system,and the performance state of the FC.Finally,experimental tests are carried out on the built-up HIL simulation platform and the physical scale down experiment platform.