Grid-tied VSI protection against grid side faults based on voltage

With gradual increase in the integration of renewable energy resources into the existing power supply network, the need for reliable and efficient grid side fault detection and protection of inverters is crucial. The existing conventional protection schemes using over-current relay is insufficient as the fault current magnitude is low for solid state devices. This paper investigates a voltage based protection scheme involving grid side fault detection along with an automatic islanding scheme of a three-phase inverter after a grid fault. After islanding the inverter will take care of its own local load and works in islanded mode until the grid fault is cleared and the VSI is again transferred to grid tied mode.