Research On Model-based Fault Diagnosis Method For Open-switch Faults Of Switch Tube Of Three-phase Voltage Source Inverters

Voltage source inverter(VSI)is an important part of the power electronic systems.Because of its low cost,high output quality and high efficiency,it has been widely studied and used in various fields.However,the inverter is the closest link between digital control and power output,and it is also a weak link where various faults frequently occur.Once the inverter system occures fault,it may cause a series of unpredictable losses.Therefore,the safe and reliable operation of the inverter is very important.Based on the model-based fault diagnosis method,this paper proposes new three-phase voltage source inverter open-switch fault diagnosis method,and builds an experimental platform based on d SPACE and RT-LAB and verifies the effectiveness of the proposed fault diagnosis method through simulation and experiment.The research content of this article mainly includes the following three aspects:(1)A new fault diagnosis method based on current observer and adaptive threshold is studied.This method only needs to utilize the signals existing in a system without the need for extra hardware.First of all,an observer is designed on the model of three-phase voltage source inverter system to estimate currents.Then,an adaptive threshold is designed on fault residuals,dynamics of the currents and variations of the system operating state.Moreover,the dead time and switching delay time are also included in the threshold to consider practical applications.Furthermore,to achieve on-line real-time diagnosis and to improve the reliability of the proposed method,the averages of the current residuals in a current fundamental period are defned as diagnostic variables.The time for this method to locate the specific faulty switch tube is 30% of the current fundamental period.(2)A fast voltage-based real-time open-switch fault diagnosis method is proposed.Firstly,for each switching period,the voltage deviation is calculated by the expected voltage and actual voltage,they are obtained via the mixed logical dynamic model and measured currents,respectively.Then,the voltage deviation of each phase is employed as a fault variable.By this way,avoiding the use of additional hardware,and embedding easily in system.Furthermore,considering the impact of sampling error,parameter error,dead time,delay time,and transition time,the adaptive threshold is designed.The time for this method to locate a specific faulty switch tube is several switching cycles.(3)A new fast open-switch fault diagnosis method for voltage source inverter employing permanent magnet synchronous motor is proposed.The estimated rotor angle is obtained through model reference adaptive system technology,and the estimated value after derivation and period average processing is used as the diagnostic variable.The open-circuit fault of the power switch in the VSI will change the estimated rotor angle;fault diagnosis can be realized by using these changes.Furthermore,an adaptive threshold is designed on dead time and delay time.This method has the characteristics of real time,short diagnosis time,simple structure,easy to insert existing control algorithms,and does not require additional sensors.The time for this method to locate the specific faulty switch tube is 15% of the current fundamental wave period.