A Skewness Based Method for Diagnosis in Quasi-Z T-Type Grid-Connected Converters

One of the very interesting converters for transformerless grid-connected PV systems is the multilevel quasi-Z T-Type inverter. Besides their multilevel operation, it presents voltage Boost capability and robustness to instantaneous switching between power semiconductors of the same leg and capability to work in fault tolerant condition. However, to ensure this capability, it is essential to ensure a fast and correct diagnosis of the component under fault. Thus, this paper proposes a new method for the detection of an open switch fault. The proposed approach uses the inverter AC line currents that will be analyzed by a Skewness based method. The method has the capability to distinguish the switch under fault. Besides that, it presents robustness to interferences such as noise, as well is insensible to variations of the injected power into the grid. Several simulation and experimental results will be presented in order to verify the capability of the proposed method.