The Study Of Solar Charging System Based On Improved DC/DC Converter

With the rapid development of the global economy, the energy cirisis and environmental issues become increasingly prominent, develop the clean and renewable energy has become the focus in the whole world. Because of its clean?safe and convenient, solar energy has been increasingly applied in various fields. Based on the advantages of solar power, considering the traditional DC charging system, an idea is presented that use solar energy as direct source to charge and each part structure of the system is designed and studied. In this paper, the power generated by the PV system is supplied directly to the charging load by the DC/DC converter, reducing the part of traditional system that charging through the inverter. Improving the system for solving the problem of system's output unstable under the influence of external conditions, and finally acheive constant voltage. The article mainly analyzed from the following aspects:First, discussing the basic principles and operating characteristics of solar photovoltaic power generating system. Considering the output of PV system can not be stable when the external environment changes, propose the design requirements that stable the system when the external conditions changes. Meanwhile, using the lead-acid battery which is now widely used in industy as the charging load, discussing the impact of the charging voltage on the battery's performance. Based on the discussion, the importance of stabling the pre-stage battery charging voltage is presented and also provide a theoretical basis for the subsequent solar DC charging system design.Secondly, designing the overall structure of solar DC charging system. Then, studing each subsytem respectively: For the pre-stage PV system, propose a control method that use the tri-state Boost to realize the MPPT control based on studing the principle of traditional Boost converter. Then verify the validity and reliability of the new control method through its corresponding circuit analyis and mathematical derivation; For the subsequent charging subsystem, proposing an idea that using the Buck converter to regulate the voltage. Based on the advantages and disadvantages of original Buck converter, design a new control method and verify the superiority and effectiveness through the simulation and experimental comparison.Finally, simulating the whole solar DC charging system. Considering the influence of external conditions, analyzing the output characteristics of the charging system. Experiments prove that when considering the changes of external factors of PV system, the designed solar DC charging system can effectively stabilize the output voltage of the battery on require suitable voltage. The system can not only regulate the voltage, but also can reduce the battery charging voltage fluctuations, thus the charging system can extend the battery life. Then, for the low frequency oscillation phenomenon of system, detailed analysis are discussed. Based on the study of the constant on-time control(COT) method, using the method to improve the charging system and then verify the validity of control method by comparing simulation results.