Unified Faults Diagnosis Method For IGBT And Current Sensor In Single Phase Casased NPC Rectifier

As a promising solution to address the issues of bulky volume and low efficiency in the conventional power frequency transformer,the power electronic traction transformer(PETT),attracts much popularity.Single-phase cascaded neutral-point-clamped rectifier(SPCNPCR)is a three-level topology of the PETT front-end input stage,which includes considerable power semiconductor devices and sensors.With this structure,the system failure rate is higher than that in the convention power frequency transformer.To ensure the safe and stable operation of the SPCNPCR,and accordingly enhance system reliability,the fault diagnosis,e.g.,power semiconductor devices and sensors,is of high importance.In this paper,the SPCNPCR is focused on,and the fault diagnosis methods,including the model-based methods and the signal-processing-based methods,are presented for SPCNPCR,aiming at achieving high-performance fault diagnosis of the insulated gate bipolar transistors(IGBTs)and sensors.In Section Ⅱ,with the operating mode and working principle the SPCNPCR,different control strategies,e.g.,the overall voltage control strategy,the voltage balance control strategy between cascaded modules,the inner-module voltage balance control strategy,the carrier phase-shifted and phase opposition disposition modulation strategy,are presented.In Section Ⅲ,the mixed logic dynamic(MLD)model of the SPCNPCR is obtained by introducing continuous variables and discrete variables.Accordingly,the task of state variable estimation,including the grid voltage,the grid current and the DC-link output voltage,is carried out.Then,the model of the IGBT and the sensor fault(e.g.,gain fault,offset fault and drift fault)is obtained.With this model,the key characteristics of two faults are elaborated.In Section Ⅳ,the residuals and its gradient are obtained through the measured signals(e.g.,voltage and current signals)and the estimated signals provided by the MLD model.According to the obtained voltage residuals,the fault identification and the fault location of the IGBT are achieved.While,by using the current residuals,the faulty IGBT and the faulty sensor can be detected in the cells.In Section Ⅴ,the performance of the proposed unified fault diagnosis method of SPCNCPR is investigated by simulations and hardware-in-the-loop(HIL)tests.From the test results,the method has the ability of accurately identifying the fault types of IGBT and current sensor and locating the faulty rectifier module.Moreover,by using the proposed fault diagnosis method,the open-circuit fault location of single or multiple IGBTs in the module can be achieved.Notice that,the gain,offset and drift faults of the grid current sensor are also effectively distinguished through the proposed method.