Study On Control Of Virtual Resistance Of LCL Grid-Connected Inverter Based On Split Capacitor Method

Grid-connected inverter is the key link of energy conversion in photovoltaic power generation system. It is the core device for converting the output of DC battery into AC power.The output AC power contains hamonic components and affects the power quality. The output filter of the inverter is responsible for reducing the harmonic effect, and its control strategy plays a very important role. In the existing LCL grid-connected inverter current control method,the use of split capacitor to join the passive damping control strategy can effectively suppress the current hannonics,but increased power loss. Therefore, based on the split capacitor method,the virtual resistance effect is realized by feedback control in order to acheve good filtering effect and reduce the loss.Firstly, the filtering characteristics of L, LC and LCL are analyzed and compared, and the mathematical model of LCL grid-connected inverter is established according to the working principle and function of grid-connected inverter. Secondly, the advantages and disadvantages of the split capacitor method compared with the traditional current control method and the influence of the addition of the passive damping on the filtering effect are analyzed emphatically. Then draw a block diagram of the split capacitor to join the passive damping control strategy,based on the control theory of virtual resistance and the equ,valent transformation principle of control block diagram, the LCL grid-connected inverter virtual resistance control based on split capacitance method is deduced on the basis of the control scheme of adding the passive damping control strategy. Finally, the simulation model based on the split capacitance method is established, and the simulation is carried out under the condition that the split capacitor branch is not damped, the series actual resistance and the series virtual resistance are carried out.The above analysis and simulation results show that, When the capacitor branch is not resistance are carried out.The above analysis and simulation results show that,When the capacitor branch is not damped when the harmonic current into the network is difficult to meet the requirements;After adding the damping,the waveform quality of the input current is obviously improved,and the harmonic ratio and the harmonic content at the resonant frequency meet the requirements less than 5% and 0.6% respectively.However,the virtual resistance control eliminates the power loss caused by the resistance,and when the circuit parameters within the positive and negative 20% of the reference value changes,the harmonic current changes little,with good robustness.