| With the development of economy, people’s dependence on batteries is increasing high. On the one hand, as the backup power for devices, batteries can meet the demands of uninterruptible power supply required by power system and play a role in loads shifting. On the other hand, the implementation of new energy vehicles is proposed in the "Thirteenth Five" plans to promote the industrialization level of electric car. Battery, as an inseparable part of the development of electric vehicles, its charge-discharge efficiency and lifespan are one of the key factors that constrains the energy storage technology of battery and the development of electric vehicles. While the researches at home and abroad prefer battery modeling, voltage and current testing and battery repairing, and the charge-discharge efficiency and lifespan of battery are seldom emphasized. The charge-discharge efficiency and lifespan are selected as research object in this paper, a set of testing charge-discharge system is proposed. On this platform, the charge-discharge efficiency and lifespan of lead-acid batteries under different policies are tested. By analyzing the testing results, control strategies to improve the charge-discharge efficiency and lifespan are acquired. The main work can be summarized in the following four aspects:(1) Analysis of electrochemical principles and fundamental parameters of lead-acid batteryElectrochemical principles during the process of charge-discharge are analyzed highly according to the internal structure of lead-acid batteries. The different control methods of the battery charge-discharging and its effects on charge-discharge efficiency and lifespan are researched. Finally, the testing methods of charge-discharge efficiency and lifespan of battery are introduced in detail.(2) Design of testing system on charge-discharge efficiencyTMS320F28335 of DSP chip is selected as control core in this system, which consists of the design of hardware circuit and the edit of software program. The hardware is composed of the design of charge-discharge unit, detection unit, drive unit and auxiliary power, while the software is divided into the design of main program, charge-discharge control program and communication program. The charge-discharge voltage and current can be set and the voltage, current, capacity and power of battery terminal are able to be displayed in this system. The information can be uploaded to upper monitor through the RS485 communication, making data management and analysis easier and realizing the test on charge-discharge efficiency of battery. Ultimately, by testing the lead-acid battery with 12V36Ah, which is used for traction (electric vehicle), the system is tested to be feasible.(3) Analysis of the impact of control strategy on battery charge-discharge efficiencyLead-acid batteries with 12V120Ah used in traction (electric vehicle) are selected as the testing object, and experimental tests are operated through charge-discharge current of 5.2A,12A,20A and 40A, obtaining the charge-discharge efficiency based on charge-discharge different currents. By analyzing the testing results, the charge-discharge efficiency can reach a maximum of 86% when the current is 20A.The fitting function is acquired in accordance with the obtained voltage and current in 20A charge-discharge strategy simulated in MATLAB. To make the charge-discharge voltage and current changed with the fitting function, the efficiency of charge-discharge can achieve the maximum.(4) Analysis of the impact of charging-discharging control policy on battery lifespanThrough testing the cycle life of batteries, the effect of different charge-discharge voltage and discharge depth is analyzed according to the experimental data. Battery lifespan based on20A discharging current is highly analyzed. The changing curve of battery capacity retention is obtained through 300 times experiments on the battery life, each including 10times capacity testing. The results show that the battery enters a stable period at 20 cycles, while the capacity attenuates sharply at 250 cycles, and reach a conclusion that the decay rates of battery life increase firstly and then decrease, and then increase again. A kind of battery lifespan testing schemes for coach electric vehicles is designed according to the results analyzed above. |
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