Research On Control Algorithm Of Grid-Connected Inverter With LCL Filter

The scale of the new energy power generation technology is enlarged day by day, the control performance of the grid-connected inverter in the grid-connected generation system affects directly the quality of electric energy into the power grid, which is extremely important in the grid-connected generation system. For reducing the harmonic content of the grid-connected current, the grid-connected inverter needs to be in series with the output filter. LCL filter has the characteristics of high frequency filtering, at the same time the system inductance value is small and the cost is low in the LCL grid-connected inverter system, as a result the grid-connected inverter using LCL filter is an inexorable trend in the alternating current output filtering link. However the LCL filter has the innate weakness, the study of the control algorithm of the grid-connected inverter with LCL filter is extremely essential. Aiming at the three-phase grid-connected inverter with LCL filter, in this paper the control algorithm is theoretical researched and analyzed, which can provide theoretical support for the control algorithm of the grid-connected inverter with LCL filter and has theoretical and practical significance. In this paper the specific work is as follows:Firstly, the basic structure of the grid-connected inverter system is briefly introduced, and the mathematical model of the grid-connected inverter with LCL filter in static three-phase coordinates, static two-phase coordinates and rotary two-phase coordinates is analyzed, at the same time the operating characteristic and the selection principle of the parameters is analyzed and a kind of parameter design method is introduced.Secondly, aiming at the grid-connected inverter with LCL filter, the single closed-loop control algorithm with grid-connected current feedback and the control algorithm with capacitor current feedback is theoretically studied, the merit and demerit of which is analyzed. On the basis of the above, a control strategy with grid-connected current feedback and network voltage feedforward is presented, which makes the system stable and reduces the number of the current sensors in the control algorithm with capacitor current feedback. The simulation results validate the effectiveness of the strategy.Then, aiming at the grid-connected inverter with LCL filter when network voltage exists harmonic, based on the analysis of the generation mechanism of the grid-connected current harmonic which network voltage harmonic results in, the quality of the grid-connected current is seriously influenced in the grid-connected inverter with LCL filter in particularly. For restraining the influence of the network voltage harmonic, the proportional resonant control is analyzed, which essence is enhancing the module value of the output impedance of the inverter. On the basis of working out the output impedance, the relation of the output impedance and disturbance restraint performance is analyzed and the parallel virtual impedance control to revise the output impedance of the inverter is introduced for restraining the influence of the network voltage harmonic. The simulation results indicate the effectiveness and feasibility of the proportional resonant control and the parallel virtual impedance control.Finally, on the semi-physical simulation platform based on RT-LAB and TMS320F2812, the above control algorithm of the grid-connected inverter with LCL filter is verified. The semi-physical simulation results validate that the control algorithm in this paper is correct and valid.