Optimal Management Of Fuel Cell/Battery Hybrid Power Systems

The hydrogen,as a kind of clean power source,is utilized in the fuel cell/battery hybrid pow-er systems(FCBHPS).The output power is supplied to the load motor after the electrochemical reaction.Fuel cell/battery hybrid electric vehicles(FCBHCVs)have gradually replaced the tradi-tional fuel vehicles as the main sustainable energy vehicle in the market,due to its characteristics of the cleanness,no pollution and zero emission,which has important value and significance for reducing air pollution and improving the level of urban environment.As an auxiliary power device,the lithium battery plays an important role in the process of system demand power mutation and start-stop.The aim of the energy management for hybrid power systems is to design a reasonable energy management strategy so that the energy utilization rate of power system and the durability of fuel cell can be improved.In this paper,based on the hybrid system structure of "fuel cell+lithium battery" in parallel,a platform of hybrid system is built for the experiments.The research on energy management strategy of hybrid system is carried out,and the relevant algorithms are verified on the experimental platform.The full combination of theory and practice is realized,and the mutual confirmation of simulation and experiment fully illustrates the proposed algorithm The effectiveness of the system.The main work and related research results are summarized as follows:(1)Finished the topology selection and vital parts selection of the fuel cell/lithium battery hybrid power system.In this paper,a hybrid system structure with affordable price and reasonable demand is selected for power management by comparing four different hybrid system topologies and analyzing their advantages and disadvantages.Based on the structure,the model,characteristics and reasonable range of common fuel cells,lithium batteries and DC/DC converters are analyzed,and the main elements of FCBHCVs are selected.The selection of core components and parameter matching of corresponding hybrid power system are completed(2)A fuzzy logic-based energy management strategy is proposed to realize the real-time energy management of the fuel cell/battery hybrid power system.In order to realize the real-time control of hybrid power system,firstly,the corresponding mathematical models of fuel cell,lithium battery and DC/DC converter are established.Based on this model and the actual control objective,the optimal solution is obtained by solving a quadratic programming problem.In this process,a fast quadratic programming solver is designed to solve the quadratic programming problem,and the convergence proof is given in detail.Considering the unknown disturbance and modeling deviation of the system,the fuzzy logic strategy is used to compensate the optimal solution online.Finally,the simulation results show that the proposed algorithm can control the output of DC/DC converter well,and the output current and power of fuel cell can be maintained near the expected value.The output current and power of the fuel cell can change smoothly under the control of the DC/DC converter,so as to reduce the damage caused by the fuel cell current mutation to the stack,prolong the service life of the fuel cell,and improve the economy and durability of the fuel cell/lithium battery hybrid power system.(3)Aiming at the problem of coordinated output of energy sources in fuel cell/lithium battery hybrid power system,a model predictive control-based power management strategy is proposed to realize the accurate control of the output power of fuel cells and lithium batteries,so that each energy source can control the output power in real time.Firstly,aiming at the problem that the load power demand of hybrid power system is unknown,a load power demand estimation algorithm based on partial least squares method is proposed.The algorithm does not need too much training data,has no additional requirements for data correlation,and has strong robustness.It can accurately predict the load power demand in time.Then,aiming at the multi-objective problem of hybrid power system energy management,the quadratic programming solver mentioned in Chapter 2 is used to solve the problem.Then,based on the basic idea of model predictive control,the rolling optimization is used to control the system in real time.Finally,the simulation and experimental results show that the proposed power management strategy can reduce hydrogen consumption by 3%,and the battery SOC fluctuation is also reduced by 16%.The output current change rate of the fuel cell is also well controlled,which will not have a serious impact on the service life of the fuel cell,so as to improve the service life of the fuel cell and enhance the economy of the hybrid power system.(4)A multi-objective charging management strategy for lithium battery pack is designed to achieve the safe and stable work of lithium battery pack,which can ensure the constraints of lithi-um battery pack and realize the safe and efficient charging of lithium battery pack.In the charging process,according to the charging constraints and energy consumption of lithium batteries,consid-ering the consistency of the state of charge of lithium batteries,the charging management problem of lithium batteries is described as a multi-objective charging problem.Then,the problem is rewritten as a quadratic programming problem by the method of weighting coefficient,and the correspond-ing charging current is obtained.In this process,an adaptive momentum gradient descent method is designed to update the weight coefficient.Finally,the corresponding simulation and experiment are designed to verify the proposed charging strategy.Compared with the previous work results,it can shorten the charging time of lithium battery pack at the same time,and under the effect of adaptive momentum gradient method,the charging time and convergence time of lithium battery pack are consistent,and the state of charge can also converge well near the expected value,which greatly improves the consistency between the state of charge of lithium battery pack(5)An experimental platform of hybrid power system was developed to verify the energy management strategy of fuel cell/lithium battery hybrid power system.Based on the analysis of the requirements of the simulation hybrid power system platform,the size,model,and parameter matching of the key components such as fuel cell,lithium battery,DC/DC converter and electronic load are determined.Then,an experimental platform was developed to verify the energy manage-ment strategy of the fuel cell/lithium battery hybrid power system.In this platform,the control strategy can be written into the host computer to control the DC/DC converter,and the correspond-ing experimental data can be monitored and collected for analysis.The experimental platform of hybrid system provides performance test and control strategy test for the research and development of fuel cell/lithium battery hybrid electric vehicles.