Voltage-Sensorless Open-Switch Fault-Tolerant Control of Three-Phase T-Type Rectifier

This article proposes a grid voltage-sensorless open-switch fault detection and fault-tolerant control for a three-phase three-level T-type rectifier. First, the parameters of the rectifier's mathematical model are estimated online. Then, changes in the estimated parameters are observed and analyzed to detect and localize the fault based on the amount of parameters' change and which parameter is changed. When a fault is detected and localized, the fault-tolerant control switches to an alternative switching function to allow the converter to operate satisfactorily. In addition, a robust control algorithm is proposed to handle all switching functions and topological changes. Unlike cascaded controllers, the proposed controller uses a single-loop control where the current reference generation and current-tracking processes are done using a single controller. The design of such a controller depends on estimating the relationship between the dc-link voltage, grid voltages, and grid currents. Experimental investigations are conducted to validate the concept and prove its high-quality operation.