Non-Intrusive Diagnosis Methods For Power Transistor Fault And Current Sensor Fault In Inverters

Power converters play key interface roles in many energy systems.However,power converters are the most vulnerable parts.Therefore,how to improve their reliability,ensure uninterrupted operation and reduce downtime is a hot topic.Fast fault diagnosis of the converter is the prerequisite for timely protection and fault-tolerant operation,and can reduce the maintenance work.Hence,it has important application value.Diagnosing power converters fast,reliably and non-intrusively,which means utilizing existing signals and avoiding extra hardware circuits,is still worth studying.In this thesis,power transistor open-circuit(OC)fault and current sensor fault of two-level inverters are studied,and four non-intrusive diagnosis methods are proposed.Firstly,a method based on phase voltage faulty characteristics is proposed for transistor fault diagnosis in the voltage loop controlled three-phase inverters.Based on fault analysis of the phase voltages,it is found that the faulty phase voltage will show low voltage characteristics in certain half periods.The method constructs a sliding window counting algorithm to detect the fault.This method only needs output voltage signals and less computation effort,which makes the method easy to apply.Compared with other methods based on output voltages,the proposed method has faster diagnosis speed and is able to diagnose double faults simultaneously.Secondly,for three-phase inverters where both output voltages and currents are sampled,a transistor fault diagnosis method based on error-adaptive threshold is proposed.After the fault analysis of bridge arm volages,the fault characteristics of brigde arm voltage deviations for differet faults are given.For three-wire inverters and four-wire inverters,the average models of bridge arm pole-to-pole voltage deviations and bridge arm pole voltage deviations are derived respectively.For the circumstance where the inductances are affected by currents,the more accurate variable-inductance average models are developed.In addition,this thesis analyses the calculation error caused by sampling error,parameter error,dead time and so on in detail,and introduces the error-adaptive flexible thresholds to ensure robustness.The proposed diagnosis method reduces the diagnosis time to several switching periods.It solves the problem that model-based methods are susceptible to the influence of the parameter and sampling errors,and makes the threshold selection much easier.In addition,two methods based on post-fault reconfiguration algorithms are proposed to diagnose transistor fault in the single-phase inverter.The fault can only be detected but not idenfied if applying the proposed method for three-phase inverters directly to single-phase inverters.The main idea of post-fault reconfiguration is reconfiguring the inverter to certain modes after the fault is detected to make the fault identifiable.Depending on whether a redundant leg is equipped or not,two fault diagnosis methods are proposed.One is based on Post-Fault Reconfiguration of Control(PFRC)and the other is based on Post-Fault Reconfiguration of Utilizing Redundant leg(PFRUR).The proposed methods improve the diagnosis speed,and are able to diagnose the fault in both inverter and rectifier modes.Proposed post-fault reconfiguration algorithm provide a new idea for fault diagnosis and have the potential to be applied to other applications or topologies.Lastly,the method for three-phase inverter transistor fault diagnosis is extended to simultaneous diagnosis of both transistor fault and current sensor fault.The faulty characteristics of these two kinds of faults are normally coupled.If only one type of fault is considered,the other kind of fault may lead to misdiagnosis.Firstly,the thesis develops the models of output line voltage deviations and phase voltage deviations,and analyzes the faulty characteristics of these votlage deviations.Then,the calculation of diagnosis variables and thresholds is derived.In addition,the asymmetry of the three-phase system is considered.The calculation errors caused by the asymmetry are quantitatively analyzed and added to the thresholds to further improve feasibility and robustness.The proposed method is the only one so far that can simultaneously diagnose both transistor fault and current sensor fault in the three-phase inverter with only two current sensors.Both faults can be diagnosed fast.