Research On The LCL Filter Characteristic Analysis And Control Of Three-Phase Grid-Connected Inverter

With the development of renewable-energy generating , the control technology of high-power grid-connected inverter has been become a hot research direction. In this paper, a dual-loop control strategy of three-phase grid-connented inverter with LCL filter is designed based on analyzing the traditional control technology of the photovoltaic grid-connected inverter.In this paper, LCL filter is analyzed that LCL filter has better performance in high-frequency harmonics suppression with less inductance comparing with L and LC filter. LCL filter not only improves the dynamic performance of high-power grid-connected inverter, but also brings down the cost of system and reduces the power loss. However,the resonance of LCL filter can cause system instability. If the resistance is connected to the capacitance, the stabilization of system is increased but the loss is produced. The method of virtual resistor has some shortcomings such as control algorithm complexity,high cost and achieving difficulty. Finally, A dual-loop current control strategy which uses grid-inductor current and capacitor current as the feed-back control variable is designed. The exterior current loop can control the grid-connected current directly and the power factor of connecting to the grid, and the capacitance current inner loop can increase the system damp and restrain the resonance. Experimental results verify that this strategy is easy to be realized and the system with lower power loss has good dynamic and static characteristics. At the same time, system modeling and stability analysis have been accomplished in this paper, and theoretical analysis has been done with Matlab.In this paper, the main circuit and the control circuit are designed in the paper based on DSP TMS320F2812. Three-phase grid-connected inverter electricity generation system is designed and built. Software is also completed. The three-phase grid-connected inverter which is desighed in this paper has achieved grid experiment; the voltage is 110 V and power is 2 kW. The experimental results show the entire system has good dynamic and static performance. In this paper, the stand-alone mode of grid-connected inverter has been researched together with soft phase locked loop.