Research Of Sine Wave Grid-connected Inverter And Control Algorithm

The developments of renewable energy and distributed power generation have been attracted more and more attentions because of the lack of energy, pollution and increasing demand of electric power. Recently, grid-connected inverter has become the cutting-edge of this field. With the background, this paper takes much effort in the hardware design, control algorithm research, simulation of the grid-connected inverter.Firstly, the topologies of grid-connected inverter system are presented, and the three-phase transformer isolated full-bridge inverter has been chosen as the main circuit structure. The model of grid-connected inverter has been analyzed., especially the bipolar SPWM circuit.The design and simulation of filter has been achieved.Secondly, the paper makes a research on the control algorithm. The PI current feedback method which has good dynamic performance is proposed by the running characteristic and the transfer function of the grid-connected inverter.A new control algorithm based on repetitive control is proposed in eliminating the theoretical error.At last, on the basis of making a sufficient study in the renewable energy applications and achievements in recent years, a 20kVA grid-connected system is designed in this paper .The paper carries out the details in control board design, drive circuit, protection circuit and the main power items calculation. A microprogramming modular is adopted in system software design. The flowcharts are all listed. For keeping the. frequency and phase synchronous to the grid, a soft PLL (Phase Locked Loop) is necessary. The block diagrams are provided in details.