Study On IGBT Fault Detection In MMC Sub-modules Based On Pulse Coupling Response

With the rapid development of flexible direct current transmission in recent years,Modular Multilevel Converter(MMC)using IGBT as the main power device is widely used.Literature statistics show that IGBT damage is one of the most common cases happening in sub-module failure.At the same time,with the continuous improvement of the voltage level of flexible HVDC projects as well as the continuous expansion of the transmission capacity,a huger electrical stress and thermal stress will be applied to IGBTs accelerating the aging process of IGBT packages.Therefore,it is necessary to study the method of IGBT fault detection in order to improve the reliability of the operation of converter valves.IGBT faults can be mainly classified into die level faults and package level faults.For now,it needs a loneger time to detect the IGBT die level faults,while its fault detection method are not compatible with the package level fault detection method,resulting a failure on package level fault detection.As a result,this paper proposes a fast,general fault detection method for IGBT based on pulse coupled response method.The following work is carried out.Firstly,based on the equivalent circuit model of IGBT with interelectrode capacitance,an IGBT fault detection method based on pulse coupling response method is proposed.The equation of gate pulse coupling response is constructed in time domain according to the IGBT equivalent circuit model,later it is verified by PSPICE simulation software and MATLAB.The fault characteristics are extracted from the response equation,accroding to which the fault detection algorithm is designed.Next,an IGBT fault detection experimental platform is built to verify the pulse coupled response method,which mainly includes an all solid-state fast edge pulse generator with adjustable pulse amplitude 0~500V,adjustable pulse width 100ns~2?s,and pulse edge within 60 ns.A MMC sub-module with a rated voltage at 600 V,a rated current at 50 A,and a storage capacitor of 10?F is also included.In the end,a pulse-coupled injection structure is designed for a half-bridge MMC sub-module.Finally,on the basis of the built IGBT fault detection experimental platform,the single IGBT off-line pulse injection experiment and the half-bridge MMC sub-module charged pulse injection experiment are carried out respectively.Experiment results shows that under the lab circumstance using the oscilliscope as the measurement tool,the pulse coupled response method can quickly detect the IGBT chip short-circuit as well as open-circuit faults within 1?s,realizing the detection of IGBT package faults at the same time,which achieves the design goal of a fast and general IGBT fault detection method.