| In recent years,the problem of energy shortage is becoming increasingly serious.Wind power generation,as an important form of new energy generation,has become the focus of attention.Compared with the large and medium-scale wind power generation systems(WPGSs),small-scale WPGSs have the advantages of lower cost,more flexible installation and a higher utilization rate of wind energy.Moreover,they can be divided into off-grid and grid-connected WPGSs.For the latter,the collected wind energy can be applied to various loads,which exhibits wider applicability.However,limited by the small and dynamic wind speed,the small-scale WPGSs collects less energy,which makes it difficult to realize the normal grid connection.Starting from the DC/DC converter topology,this paper mainly studies a topological transformation converter with high efficiency,high voltage gain and wide voltage range for small-scale grid-connected WPGSs.Furthermore,to approach the challenge of output voltage instability during the mode-switching processes,a corresponding mode switching control method is proposed to achieve smooth switching between multiple modes.The main works are organized as follows:(1)A variable-structure multi-resonant soft switching DC–DC converter is proposed.Adopting the idea of topological transformation,this converter realizes flexible conversion of resonant tank structure by reasonably controlling the on/off of two auxiliary switches.Ultimately,the resonant tank of the converter can operate in two different modes.For the inveter unit,it can operate in full bridge or half bridge mode,respectively.Selecting the working modes reasonably,the converter can obtain good effect of widening the voltage gain range.Moreover,by using the fundamental equivalent analysis method,the circuit models of the two typical working structures are deduced and analyzed in detail,and the important formulas related to the operation parameters of the converter are obtained.In addition,the modal analyses related to operation of the two circuits are carried out in detail.(2)A parameter design method suitable for the variable-structure DC/DC converter is proposed.By using this parameter design method,the resonant frequency point and peak gain point is designed reasonably.Furthermore,with the reasonable control of the working mode,the good resonant characteristics,such as high gain and high efficiency,is obtained.Finally,the proposed converter can meet the application requirements of high gain,wide input voltage range and high efficiency conversion in a narrow frequency range.(3)A transient switching control method for the variable-structure converter is proposed.This method adopts the idea of gradual regulation.And the incremental/decreasing operation of duty cycle of the control signal of the switch is realized by gradually adjusting the comparative value of the control signal of the corresponding switch.Consequently,it effectively reduces the larger fluctuation of the output voltage caused by the mode switching process,and helps to realize smooth switching.(4)The relevant experimental design and verification are carried out in this paper.Based on the parameters obtained from theoretical analysis,a 200 W test prototype is built,and the feasibility of the proposed variable-structure multi-resonant soft switching DC–DC converter and the effectiveness of its mode switching control method are verified. |
PDF Full Text Request