| As a clean and efficient power source,fuel cells have received great attention and development in recent years.As one of the research hotspots,the multi-fuel cell stack system has the advantages of high efficiency,excellent economy and strong fault tolerance.In the current multi-stack system research,in order to achieve independent control of the output power of a single stack and make the stack output voltage consistent with the bus voltage,a DC/DC converter needs to be connected in series with each branch,but this will increase the system cost,weight and volume.Therefore,this paper selects a dual-stack architecture scheme without DC/DC on the branch as the research object,uses experimental methods to verify the feasibility of the scheme,and studies the energy management strategy suitable for the power system with this architecture.The main research contents and results of this paper are as follows:Firstly,dynamic and transient experiments are carried out under different loads for the dual-stack series and parallel architectures without DC/DC on the branch.The dynamic experimental results show that the voltage difference,voltage overshoot and undershoot rates between the dual stacks in the series structure and the current difference between the dual stacks in the parallel structure are positively correlated with the load,The power adaptive distribution output between the stacks under different schemes is related to the performance of the stack itself.The outputs of the two stacks are stable during continuous operation and there is no mutual interference phenomenon.The transient experiment found that the current overshoot is an important reason for the output fluctuation of the dual stack,when the dual stack works under different loads,the current and voltage overshoot time is short and within 50 ms.The experimental results prove that the series and parallel architectures without DC/DC on the branch can run stably and respond quickly.Secondly,the forklift is selected as the application object of the dual fuel cell stack system.In order to obtain the real working condition data,the items of acceleration,maximum speed,parking lift,full load climbing,full load cycle and half load cycle were tested,and a 1-hour comprehensive data were integrated by national standard guidance as the simulated input power.Then,a dual fuel cell stack electric-electric hybrid system for forklift trucks is constructed,and the key components in the power system,such as battery,fuel cell stack and bus DC/DC,are modeled.In this paper,the energy management adopts a layered model.For the top-level energy management between the dual fuel cell stack and the battery,three strategies of charging,fuzzy division and interval power follow are proposed.The underlying energy management strategy within the dual fuel cell stacks aims at optimal efficiency.Finally,simulations are carried out under different conditions,and the Newton iteration method is used to solve the adaptive power distribution within the dual stacks.The simulation results show that although the power following strategy can maintain the SOC in a stable range,the power output of the fuel cell changes frequently.In contrast,the charging and fuzzy partition strategies are better for the health protection of the fuel cell.In addition,the equivalent hydrogen consumption of the system under the high initial SOC and series scheme is lower,and the fuzzy partition strategy can reduce the hydrogen consumption by 9.84% per cycle at most.Compared with the single-stack scheme with the same performance,the dual-stack scheme can reduce the hydrogen consumption by1.6245‰ per cycles at most.Mathematical analysis proves that in the concave region of the polarization curve and the performance difference of the two stacks increases with the increase of the output current,the efficiency of the parallel connection of the two stacks is better. |
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