Research And Realization Of A DC-DC Converter Of Single-Phase Transformerless PV Inverter System

For the development of global economy, the demands to energy are increasing day by day and the shortness of energy draws more attention than any time before. Solar energy is commonly accepted because of its advantages such as economy and cleanness.Solar power is the most important means of solar energy application.The most commonly used inverter includes all systems employing isolating transformers that can be installed either in the output of the inverter or between intermediary stages.The first approach requires low-frequency designs resulting in increased size, weight and cost,no conducive to miniaturization and widespread promotion. To deal with such disadvantages, multistage converters were proposed; allowing the use of high-frequency transformers. Despite the significant reduction of weight and volume, such alternative affects negatively the efficiency and implies higher costs due to the increased complexity and amount of semiconductors.The thesis have come up with a new Photovoltaic inverter without transformer,which can transform the power from solar panels into DC-DC converter, and then DC-AC inverter, transport the electrical energy to the electrical network.The elimination of the output transformer from grid-connected photovoltaic (PV) systems not only reduces the cost,size, and weight of the conversion stage but also increases the system overall efficiency,which has been widely used in foreign countries.This paper focus on the DC-DC converter of the transformerless single-phase photovoltaic(PV) inverter,short for PV-DC_DC converter. The digital control system of PV-DC-DC converter was designed,based on DSP2812and CPLD,improved the control accuracy and efficiency.This thesis elaborated the operating mode and the principle of the Boost Converter and the relationship corresponding to the input and the output,analyzed of the advantages and the disadvantages of this circuit,made the improvement combining with the actual situation of this system.Then selected the improved Boost ZVT-PWM circuit.The experimental results proved that the main switch and auxiliary switch in the new circuit achieved the soft switching and improved the transmission efficiency.This thesis analyzed the commonly used MPPT algorithms,compared the advantages with the disadvantages,on this basis,given improvement program respectively.Combining with the actual situation of this system,this paper proposed improved perturbation and observation method,The result showed that the algorithm started quickly, tracked accurately.Finally,this thesis designed the hardware and the software of this system to realize the anticipated function.The converter experimental prototype was completed and the result show that main circuit’s parameters was right,was achieved and converter’s work was stable.It is economically and socially significant.