Design and Research on the LCL Filter in Three-Phase PV Grid-Connected Inverters

Abstract

With the energy crisis and environment revolution are becoming more and more serious, renewable power generation system is drawing more and more attention. We vigorously developed clean energy such as wind, and solar power. The control technology of grid-connected inverter is the key technology in renewable power generation. In the grid-connected inverter, the all-controlled power electronic devices IGBT and GTO are be used, which is modulated by the high frequency PWM. As the result, the du/dt and di/dt are ever large. Due to the presence of some vagrant parameters, the current included high order harmonic flow into the power grid, which made the harmonic pollution. The most common filter is L in the grid-connected inverter. In order to decrease current ripple, the inductance have to be increased. As a result, the volume and weight of the filter increased. Although the structure and the parameter of the LC filter are easy, the filtering effect is not good because of the uncertainty of network impedance. LCL filter had an inherently high cut-off frequency and strong penetrating ability in low frequency. So LCL filter has come into wide use in the inverter. What is the most difficult is that how to select the parameter and control resonance. In this paper, with the three-phase PV grid-connected inverters topology, firstly analyze the inductance, the ration of two inductances, selecting the filter capacitor and resonance resistance. Based on these theories, a LCL filter is designed. The simulation result proved that the LCL filter achieve the best performance, and indicated the impacts on the stability and filtering property from the parallel resistor or