Robust Control Scheme for a Three Phase Grid-Tied Inverter With $LCL$ Filter During Sensor Failures

This article discusses the operation of a three phase grid-connected inverter with LCL filter under an unbalanced/distorted grid voltage condition. Two case studies are considered in this article that relate to the operation during grid side current and voltage sensor failure. First, a case study showing the operation of the inverter during a grid side current sensor failure is discussed. Second, a case study showing a grid voltage sensor failure is discussed. For the grid side current sensor failure methodology is developed and discussed to estimate the grid current from the sensed inverter current and the capacitor voltage reference. For the grid side voltage sensor failure, an internal model based grid voltage estimation architecture is proposed, and both its local and global stability analyses are presented. The controller design is based on the Lyapunov energy function, and its derivation during the two types of sensors failure have been discussed and presented along with a detailed mathematical analysis. The proposed architecture is verified on a reduced-scale laboratory prototype, and various case study results are presented.