Study On High Voltage Gain Power Converter To Suppress Low-Volatage Solar Power Fluctuation

The14th Five-Year Plan of China has pointed out that it’s necessary to further promote the large-scale and high-quality development of new energy generation,and it is mainly based on photovoltaic power generation.Therefore,the related research on photovoltaic power generation becomes particularly important.In photovoltaic power generation,the solar energy is boosted and collected to the DC bus through the step-up converter,and then realize girdconnected by inverter.However,due to the fluctuating and intermittent feature of photovoltaic power generation,there are three key problems hindering its development.Firstly,the output voltage of photovoltaic power generation is too low for interfacing DC bus,therefore high voltage gain DC-DC converters are required.Secondly,it’s necessary to realize converter voltage regulation for DC bus voltage stability because of the solar power fluctuation.Finally,the solar power fluctuation may cuase the instability of gird-connected photovoltaic power generation systems.Aiming to solve above problems,this dissertation carries out study on high voltage gain power converter to suppress solar power fluctuation.The main contributions of this dissertation are as follows.（1）A family of embedded Z-source DC-DC converters（EZSCs）are proposed for photovoltaic power generation.EZSCs realize high voltage gain and low stress by adding a diode and a capacitor into the traditional Z-source DC-DC converter and changing the position of the input power supply.One of EZSCs is analyzed and verified from two aspects include high voltage gain and low stress as a typical case,which well validates the innovation and effectiveness of proposed EZSCs.（2）A stacked boost embedded Z-Source DC-DC converter（SBEZSC）is proposed for DC bus voltage stability.Specifically,the construction method of stacked boost converter（SBC）is used to transfer the task of converter voltage regulation of high voltage gain DC-DC converter to another easy control converter.Hence,the control design of high voltage gain DC-DC converter has been simplified through topology design.The proposed SBEZSC is verified through theoretical analysis and experiment,which also verifies the innovation and effectiveness of this topology design method.（3）In order to realize stability of grid-connected photovoltaic power generation systems,an impedance-network-based electric spring（INES）is presented,which consists of a switched inductor impedance-network-based inverter.The proposed INES can solve the problems of high input voltage and shoot-through state of the inverter bridge arm in traditional electrical spring,and realize voltage stability of grid-connected photovoltaic power generation systems.The creativity of this dissertation can be listed as,i.e.,proposals of（1）high voltage gain power converter to suppress solar power fluctuation;（2）a method of topology design to simplify control design of high gain DC-DC converter to realize DC bus voltage stability;and（3）an impedance-network-based electric spring to realize voltage stability of grid-connected photovoltaic power generation systems.