In order to increase the reliability and availability of wind turbines, condition monitoring and fault diagnosis are considered crucial means to achieve these goals. In this context, wind turbines based on permanent-magnet synchronous generators (PMSGs) with full-scale power converters are an emerging and promising technology. However, several statistical studies point out that power converters are a significant contributor to the overall failure rate of modern wind turbines. Accordingly, this paper presents a new and simple method for open-circuit faults diagnosis in full-scale back-to-back converters, applied in PMSG drives used for wind turbine systems. The three phase currents carry information about the faults and hence are used to diagnose the faults in the system. The three phase currents of the generator side and grid side converter are taken as the input for the fault detection. When the current value is zero it indicates that there is an open circuit fault in the particular phase. This concept is used to identify the faulty phase and the faulty switch. It is seen that the proposed method does not require any voltage and current sensors hence reducing the system complexity and the cost of the drive.