Research On Control Strategy For Single-phase Grid-connected Inverter With LLCL Filter

With the rapid development of the world economy, the demand for energy is growing,limited traditional fossil energy resources, especially for new energy research and efficientuse of wind and solar and other renewable energy sources has put forward higherrequirements. Distributed power generation system is an effective way of new energyutilization and conversion of electrical energy grid inverter has played an important role inthe grid to transport electricity. This paper studies the single-phase inverter LLCL andnetwork control technology.And LCL filter as fourth-order LLCL filter has good high-frequency harmonicsuppression, the total inductance required is relatively small. While at the same grid currentstandard conditions, network-side inductor of LLCL filter reduces largely, reducing systemcost and inductor size. This paper analyzes the inverter output voltage harmoniccomposition, detailed the design process parameters fourth order LLCL filter.LLCL filter resonant peak problem also exists through the filter element in the passivedamping damping resistor series-parallel method can weaken the damping peak, but it willbring power loss. Only the control algorithm, based on the equivalent capacitor currentfeedback active damping method, has been widely used. A novel method of mixing has alsobeen some damping use.This paper analyzes the mechanism of passive damping and active dampingcoefficient and obtained feedback inhibition effect relationship, and a brief introduction ofhybrid damping methods.In the analysis of low frequency characteristics of the resonant impedance of the largerbranch, similar to open, so the grid system similar control method LLCL filter and LCLfilter. This paper analyzes QPR control with harmonic compensation, the influence ofparameters on the closed-loop control system, and select parameters; addition, according to the stability margin and network system design parameters pi controller based. Simulationresults show the effectiveness of the two control algorithms. Finally, a simple analysis ofthe effects of harmonics on the grid voltage and grid current, introduced before theapplication of feed-forward strategy.