Research On Floating-output Interleaved-input DC-DC High-gain Three-level Converter In PV System

The high gain DC/DC converter are widely applied in many fileds,such as PV system,because of its high gain and high efficiency.What's more,in order to improve the reliability and power generation efficiency of PV system,the high gain DC/DC converter should increase its voltage gain and efficiency.In a word,it is great important to do a systematic search for the high-gain high-efficiency unisolated converters.In this thesis,a kind of floating-output interleaved-input three-level high-gain DC/DC converters(TL-FIBC),apt to high voltage occation,is introduced.Because of the suspension interleaving connection form and the three level structure,TL-FIBC has the advantages of low voltage stress and small current ripple.What's more,the working principle of TL-FIBC is analyzed in detail.In order to improve the steady-state and dynamic performance of the system,the mathematical model of TL-FIBC is established by the state space averaging method.In addition,it is necessary to design the voltage regulator and current regulator.The strategy of flying capacitor equalizing voltage is adopted to make the voltage of the flying capacitor of upper and lower bridge arm equal.In PV system,the strategy of Maximum Power Point Tracking(MPPT)is widely used to enable the PV batteries to work at MPP with Maximum Power Output.The perturbation and observation method is used to realize maximum power tracking.And we have to design the period lengths and stepsize of perturbation reasonably to cut down the oscillation of the stable state point,as well as make the dynamic response fast.Finally,the control method is chosen as the MPPT control strategy based on input parameter perturbation and observation in this thesis.In order to verify the correctness of the theoretical analysis and the feasibility of the proposed control strategy,a complete 2.5kW verification platform of TL-FIBC is constructed to verify the function of the system.Then,we finish the experiment at a 60 V input to 700 V output,the experiment of power level at 2.5kW switch to 1.25 kW,voltage regulator experiment of the flying capacitor,the experiment of efficiency test,and the experiment of MPPT.The experiment wave and data processing result show the great feature of high gain and high efficiency.