Research On Low Voltage Ride Through Of Three-phase Solar Inverter Based On Virtual Resistor

This article mainly studies on the design of the three-phase grid connected inverter. Basic principles of a three-phase inverter have been analyzed, so have the details of designing one, including the drivers of IGBT bridges. Further, the article proposes some optimization to the traditional inverter.Firstly, a model of a three-phase inverter is proposed. Basic structure is set, and the value of elements can be determined under different prerequisite decided by the operation condition of the inverter. As the power of an inverter is always high, the article presents a design of IGBT driver with different function of protection, which includes the protection in short circuit, overcurrent, overheating, undervoltage. As for the control methods, PI control under dq axis is used.Secondly, this article proposes the design of virtual resistors. Generally, resistors are added to LCL filters to check the resonant peaks. Virtual resistors are the method of adding parameters to control loop to make sure the inverter work stably even when resistors are eliminated.Thirdly, this paper illustrates the design of PLL when LVRT happens. When grid voltages drop unbalance, the PLL is the key to handle with this situation. In this paper, the design T/4is used to extract positive sequence voltage, so that the PLL can work stably. What’s more, the influence of harmonics on the PLL can be suppressed by the selective design of eliminating harmonics. MATLAB simulation confirms the validity of the design.Finally, an experimental platform is established. The experimental result testifies the correctness of the design. Further expectation is proposed.