Wide Input Voltage Range DC/DC Converter For Photoltatic System

With the energy crisis and environmental pollution become more and more important,distributed power gets more and more attention as a renewable energy, among photovoltaic(PV)grid power generation develops most rapidly in recent years. DC/DC converter is an important part of the two stage grid connected generation system. However, under the influence of climatic conditions,solar panels have a wide range of output voltage. Therefore,it is of great value to study the high efficiency?low loss wide range DC/DC converter in photovoltaic system.Full-bridge LLC resonant converter has the advantages of achieving zero-voltage-switching for all the power switches and zero-current-switching for the output rectifier diodes in the whole load range, and capable of regulating voltage, so it is a promising topology for DC/DC converter. For the problem of LLC resonant converter applied in wide input voltage range application, on the basis of full bridge LLC resonant converter, a novel constant frequency phase shift control method which is based on the combination of the primary side-phase shift(PS-PS) and secondary side-phase shift (SS-PS) is proposed in this paper. If the input voltage decreases, SS-PS control is adopted, whereas the input voltage increases adopts PS-PS control.In this paper, the operation principles and characteristic under PS-PS mode and SS-PS mode are presented in detail, the influence of LLC resonant converter secondary side-phase shift mode-variance upon inverter working states is discussed. The circuit design scheme and parameter design are given. To further verify the feasibility of the circuit topology and control strategy. Simulation model is established based on Matlab/Simulink as well as an experimental prototype is designed based on TMS320F2812. Simulation and experimental results show that:(1) The operating frequency of the converter is constant and always works at the resonant point,and it has good performance under either PS-PS mode or SS-PS mode, the switches of inverter are ZVS on, the switches of rectifier side are ZVS off and rectifier diodes are ZCS off; (2)The working state of the inverter changes with secondary side-phase shift mode-variance. For leading mode, the inverter works in inductive state; and for lagging mode, with the increase of phase shift angle, the inverter state changes from inductive to capacitive.