Research On Fault Diagnosis And Fault Tolerance Of Three-phase Inverter

In recent years,three-phase inverter has been widely used in microgrid,photovoltaic industry,rail transit and other fields due to its important function in the power field.However,the power device in the inverter is prone to failure.Once the power device is faulty,it will bring economic loss and threaten system security.In order to improve the security and reliability of the system,the fault diagnosis method and fault-tolerant control strategy of three-phase inverter are studied in this paper.Aiming at the problem that multiple measurement devices are required for voltage-based fault diagnosis methods,this paper firstly analyzes the variation of the midpoint voltage of the three-phase inverter before and after the fault,and then proposes a fault detection method based on the midpoint voltage between DC side and AC side.But the detection results can only preliminarily determine if the faulty tube is upper or lower.Therefore,a diagnosis method based on structural transformation is proposed.In this method,the inverter is transformed several times to make the midpoint voltage appears new fault characteristics in the new circuit structure,so as to locate the fault tube.Based on capacitance and pulse,two transformation methods are proposed for diagnosis,both of them can quickly diagnose the open-circuit fault of a single power tube and reconstruct the circuit.to restore the normal operation after diagnosis.In order to improve the range and speed of diagnosis,this paper analyzes the change of the midpoint voltage of the three-phase inverter in the case of single-tube faults and double-tube faults,and then proposes a fast fault diagnosis method combined with the switching function.On the basis of using the proposed fault detection method based on midpoint voltage,the diagnosis method uses the switch state to increase the fault characteristics,so as to realize the location of the fault tube.The switching state is easy to obtain from the system,so this method only needs to detect the midpoint voltage.Compared with the previous diagnosis method based on switching function,it reduces the use of sensors and can realize the diagnosis of all single-tube and double-tube faults.In order to make the three-phase inverter work stably after fault,it is usually necessary to use the fault-tolerant control strategy.The current research direction is to enhance the reliability and expand the fault-tolerant range,but the increase of this range will also increase the use of the devices.Aiming at this problem,a new fault-tolerant inverter topology is proposed,which utilizes the DC side capacitors to convert the circuit into a three-phase four-switch structure to achieve fault tolerance.And for the fault-tolerant structure,a control strategy based on the voltage compensation is also proposed,which can effectively suppress the DC side capacitor voltage offset.This proposed fault-tolerant strategy has the characteristics of using less devices,large fault tolerance space and can also achieve secondary fault tolerance.Finally,the proposed methods are verified by Matlab/Simulink,which proves the effectiveness of these methods.